User Bit Research Articles

Parallel Writing and Detection for Two Dimensional Magnetic Recording Channel

Two-dimensional magnetic recording (TDMR) is treated as the next generation magnetic recording method, but because of its high channel bit error rate, it is difficult to use in practices. In this paper, we introduce a new writing method that can decrease the nonlinear media error effectively, and it can also achieve 10 Tb/in2 of user bit density on a magnetic recording medium with 20 Teragrains/in².

Performance analysis of two-dimensional optical code-division multiple-access systems using novel multi-code pulse-position modulation

Previous works show that pulse-position modulation (PPM) is an effective signalling method for mitigating multiple-access interference, and hence is able to increase the number of users in two-dimensional (2-D) optical code-division multiple-access (OCDMA) systems. However, in order to achieve high bit-rates, 2-D OCDMA systems using PPM signalling require very high transmitted power because of the negative impact of dispersion. In this study, the authors propose a novel modulation technique of multi-code PPM (MCPPM), which is the combination of the PPM and multi-code modulation (MCM). As the proposed technique inherits advantages from both MCM (in mitigating the dispersion) and PPM, 2-D OCDMA systems using MCPPM signalling are able to support higher user bit-rates for a larger number of users at low transmitted powers. Numerical results show that 2-D OCDMA systems using 4-4-MCPPM can support 60 users with 5 Gbps per user at the transmitted power of −7 dBm. The power gain in this case is 11 dB compared to 2-D OCDMA systems using 4-PPM signalling. The proposed systems using 4-2-MCPPM can support as many as 36 users with the bit-rate of 10 Gbps per user and transmitted power is −2 dBm.

On Symbol Mapping for Binary Physical-Layer Network Coding with PSK Modulation

In a system employing physical-layer network coding, the superimposed constellation at the relay may have ambiguity where one received signal is associated with more than one possible combination of users' data. We find the necessary and sufficient condition on a user bit mapping which removes this ambiguity for phase shift keying modulation. Further, we introduce the concept of semi-Gray mapping which improves the system BER performance and achievable rate. The necessary and sufficient condition of having a semi-Gray mapping is also found. Interestingly, the widely used binary reflected Gray mapping does not satisfy the semi-Gray mapping condition resulting in a poorer performance compared to our proposed semi-Gray scheme.

Joint Level 2 and 3 Dynamic Spectrum Management for Upstream VDSL

Dynamic spectrum management (DSM) refers to a wide range of techniques for counteracting crosstalk in digital subscriber line (DSL) networks. DSM is categorized into three levels based on the degree of coordination among users. In this article, we investigate optimal joint level 2 and 3 DSM for upstream DSL. We will discuss the difficulties of finding the universally optimal solution and we propose an optimal algorithm, referred to as IF/MAC-OSB, under some practical and implementation assumptions for this problem. Using computer simulations, we show that IF/MAC-OSB is capable of increasing the user bit rates considerably compared to several other DSM techniques. The proposed algorithm involves using the minimum mean squared error (MMSE)-generalized decision feedback equalizer (GDFE) together with Lagrange dual optimization. We address several aspects of the problem including the optimal decoding order in the GDFE receiver, GDFE error propagation, and the computational complexity of the algorithm. We also study effects of channel model randomness and upstream power back-off utilization on the performance of the algorithm.

A Two Stage Stochastic Semidefinite Relaxation for wireless OFDMA Networks

Abstract In this paper, we propose a two stage stochastic binary quadratic program for OFDMA wireless networks. The aim is to minimize the total power consumption of the network subject to user bit rates, sub-carrier and modulation constraints. We derive from the quadratic model a linear (LP) and a semidefinite programming (SDP) relaxation. Numerical results show tight and near optimal bounds for the SDP relaxation.

Multi-User Detection Techniques for DS-CDMA UWB System

Ultra-wideband(UWB) is currently one of three new technologies of wireless communication. Multi-user detection technique is mainly used to eliminate multiple access interference（MAI）in DS-CDMA UWB communication systems. Linear multi-user detection algorithm for multi-access interference suppression or even elimination has certain results. But for a fixed decision threshold is set to 0, the detection performance of linear multi-user detection algorithm will be decreased significantly. Therefore a kind of multi-user detection with pre-processing has been researched. Through the pre-processing, we set dynamic threshold to direct decision the user's data bit information so as to solve the problem the linear multi-user detector’s decision threshold which is fixed impact the detection performance. We may get the global optimal solution though pre-processing of using the thought of the branch and bound algorithm and forcing rules. Then the original problem changes into a smaller multi-user detection problem, in order to get the aim of reducing MAI, increasing the probability of a correct decision and reducing the bit error rate. From the simulation experiment results, it is shown that it has a significant effect in system detection, because after pre-processing the probability of a correct decision has increased, and the bit error rate has been reduced.

Reducing the Dispersion Effects in Multiwavelength Optical CDMA Systems by Using MCM Signaling

We propose a novel multiwavelength optical code-division multiple-access (OCDMA) system using multicode modulation (MCM) signaling. For the multicode demodulator, we employ a maximum-likelihood detection and optical hard limiters. The work in this paper theoretically analyzes the performance of the proposed system over linear dispersive channels, while taking into account the impacts of multiple-access interference (MAI), optical-beating interference (OBI), and receiver noise. It is seen that the use of MCM can significantly relax the effects of chromatic dispersion. In addition, MAI and OBI can be effectively mitigated in the proposed system. As a result, in comparison with the conventional systems using on-off keying (OOK) modulation and pulse-position modulation (PPM), the proposed system can support a higher user bit rate and a larger number of users. Also, a lower transmitted power is required and a longer transmission length can be achieved.

Signal Processing for Near 10 Tbit/in$^{2}$ Density in Two-Dimensional Magnetic Recording (TDMR)

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Two-dimensional magnetic recording (TDMR) is a new magnetic recording paradigm that aims to record one bit of information in one or a few grains, with the goal of achieving a recording density of nearly 10 Tbit/in<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex></formula>. In addition to the usual noise, a TDMR channel experiences the problem that some bits are never recorded because of the randomness of grain size and location. Thus, it is believed that a key component of a TDMR channel is two-dimensional (2-D) signal processing along with a strong error correction code. In this study, the TDMR channel is investigated based on a random Voronoi grain model and a signal processing architecture is proposed. Here, a 2-D linear minimum mean squared error (LMMSE) equalizer and a low-density parity-check (LDPC) code are employed and the effects of unwritten bits are modeled by a Gaussian mixture model. In numerical simulations, the proposed architecture shows the feasibility of user bit densities near 10 Tbit/in<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex> </formula> for media with a 20 <formula formulatype="inline"><tex Notation="TeX">${\rm Tgrains/in}^{2}$</tex></formula> grain density. </para>

Channel Modeling and Capacity Bounds for Two-Dimensional Magnetic Recording

Two-dimensional magnetic recording (TDMR) differs from traditional track recording in that the bit-size-to-grain-size ratio is drastically reduced so that the channel bits are roughly of the same sizes as those of the magnetic media grains. This is envisioned to be achieved by shingled writing, a write-process in which the corner-writer partially overwrites the previously written adjacent track, effectively writing very closely spaced narrow tracks with no guard bands. Since the tracks are very narrow, they can be read by an array of read-elements whose spacing is equal to the narrow track pitch, creating a two-dimensional (2-D) array of readback signals (the two dimensions being the cross-track and the down-track dimensions). In the absence of an array of read elements, the same 2-D readback can be obtained by progressive scans of a single read element that reads one narrow track at a time and stores the readback signal in a 2-D array. In this paper, we present simple magnetic grain media models and shingled-write process models that capture the essence of TDMR. We assume that the granular recording medium consists of randomly shaped tiles (each tile represents a grain), randomly covering the medium plane. We then derive a suitable 2-D read/write process model. Using proper information-theoretic inequalities and bounding techniques, we derive methods to bound the capacities of TDMR channels. The results reveal that information capacities in excess of 0.6 user bits per grain are possible to attain over TDMR channels.

A Survey of Scheduling and Interference Mitigationin LTE

Among the goals of 3GPP LTE networks are higher user bit rates, lower delays, increased spectrum efficiency, support for diverse QoS requirements, reduced cost, and operational simplicity. Resource scheduling and interference mitigation are two functions which are key to achieving these goals. This paper provides a survey of related techniques which have been proposed and shown to be promising. A brief discussion of the challenges for LTE‐Advanced, the next step in the evolution, is also provided.

Robust Underwater Telemetry With Adaptive Turbo Multiband Equalization

In this paper, a multicarrier modulation scheme is presented for acoustic communication at low signal-to-noise ratios (SNRs). User bits are put through a rate 1/3 turbo encoder and interleaved with periodic training bits. A maximal-length sequence is prefixed for signal detection and equalizer convergence, and the resulting bit stream is simultaneously modulated onto multiple phase-shift keyed carriers. Since each subband carries the same symbol sequence, the baseband ensemble is amenable to multichannel equalization. An adaptive multiband equalizer is thus constructed for joint equalization and despreading of the frequency bands. Iterative equalization using soft information from the turbo decoder further enhances the receiver performance. A reduction in complexity is achieved by equipping the subbands with separate recursive least squares tap updates, yet guided by a common error signal. The proposed algorithms are tested on acoustic data from the Baltic Sea, using eight subbands of 460 Hz each, at an effective data rate of 75 b/s. Robust receiver operation is demonstrated at overall receive SNRs down to - 12 dB in three different channels, which corresponds to an SNR per bit <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Eb</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =+ 5 dB.

Duty-Cycle Division Multiplexing: Alternative for High Speed Optical Networks

Performance of 3×10 Gbps duty-cycle division multiplexing (DCDM) is analyzed. The channel demultiplexing is performed electronically at single user bit rate (10 Gbps). At 30 Gbps, null-to-null spectral width of 80 GHz is measured for DCDM technique which is 33.3% less compared to 30 Gbps conventional return-to-zero (RZ). In this system, the worst channel required a receiver sensitivity of around -25.6 dBm at bit error rate (BER) 10-9. The chromatic dispersion tolerances of the system are 210.5 and 236 ps/nm for the worst and the best channel respectively.

Duty-cycle division multiplexing (DCDM)

A multiplexing technique, which is based on duty-cycle division, is proposed. The channel multiplexing and demultiplexing are performed electrically at the single user bit rate, which is very economic. In a three-user system (3×10 Gb/s), the simulation results show that the best receiver sensitivity value achieved is −30.1 dBm with an optical signal-to-noise ratio (OSNR) of 22.3 dB, while the chromatic dispersion tolerance ranges from 192 to 280 ps/nm. Migration from 30 to 120 Gb/s is achieved with the penalty of 6.4 and 5.2 dB in the receiver sensitivity and OSNR, respectively, for the worst user.

Spectral Efficiency Study of Two Multirate Schemes for Asynchronous Optical CDMA

Multirate transmission techniques, such as multiple-code (MC) and multicode-keying (MK) schemes, have been proposed for asynchronous optical code-division multiple-access (O-CDMA) systems supporting multimedia services. A user in the MC scheme transmits several codes at the same time to represent the transmission of several data bit ones. The number of parallel codes transmitted at a time is proportional to the user's bit rate and the number of data bit ones. While the MK scheme only transmits one code at a time, each code represents a symbol and each transmitted symbol represents multiple data bits. Data rate is varied by changing the symbol size, which, in turn, changes the number of data bits per baud, similar to MODEM communications. In this paper, the spectral efficiencies (SEs) of these two asynchronous schemes are derived for the comparison of their performances and efficiencies as a whole. The SE of the conventional single-rate on-off-keying (OOK) O-CDMA scheme is also derived for a baseline comparison. Our numerical results show that the MC scheme always has a better SE than the single-rate OOK scheme, while the MK scheme can have a better SE than the single-rate OOK scheme under certain conditions.

High-Voltage Multicarrier Spread-Spectrum System Field Test

High-voltage (HV) power lines have been used as a communications medium since the 1920s. Those point-to-point links were typically based on single-sideband amplitude modulation. These days, the state of the art in HV power-line carrier (PLC) communications comprises the combination of analog systems, mainly for teleprotection tasks, and digital systems, used for voice and data transmission. Beside traditional core services (monitoring, operation management, and limitation and removal of failures), electrical utilities would like to satisfy the increasing need of new internal applications. In that way, quadrature amplitude modulation and, most recently, multicarrier modulation (MCM)-based modems are beginning to play an important role in HV PLC systems. Although the typical 4-kHz bandwidth has been recently increased up to 32 kHz, this paper proposes a low-power 256-kHz bandwidth multicarrier-spread-spectrum (MC-SS)-based physical layer. Based on channel measurements, the MC-SS symbol has been designed and tested in order to increase the user bit rate while delivering reduced power spectral density and bit-error rate.

Obtaining FPGA soft error rate in high performance information systems

Soft errors due to cosmic particles are a growing reliability threat for VLSI systems. The vulnerability of FPGA-based designs to soft errors is higher than ASIC implementations since the majority of chip real estate is dedicated to memory bits, configuration bits, and user bits. Moreover, Single Event Upsets (SEUs) in the configuration bits of SRAM-based FPGAs result in permanent errors in the mapped design. FPGAs are widely used in the implementation of high performance information systems. Since the reliability requirements of these high performance information sub-systems are very stringent, the reliability of the FPGA chips used in the design of such systems plays a critical role in the overall system reliability. In this paper, we compare and validate the soft error rate of FPGA-based designs used in the Logical Unit Module board of a commercial information system with the field error rates obtained from actual field failure data. This comparison confirms that our analytical tool is very accurate (there is an 81% overlap in FIT rate range obtained with our analytical modeling framework and the field failure data studied). It can be used for identifying vulnerable modules within the FPGA for cost-effective reliability improvement.

Bimodulation code for signal waveform modulation multilevel optical disc

A new method for implementing a multilevel run length limited (ML-RLL) modulation code used in a signal waveform modulation multilevel (SWMM) optical disc, termed bimodulation code (BMC), is proposed. BMC is implemented with two steps: run length modulation and level modulation. A code rate of 5/6 BMC is realised, and the code efficiency reaches 94.47%. The parameter user bits per 400 nm of the presented code is 1.96, which is 30.7% more than that of EFMplus code used in a DVD system.

Soft Error Susceptibility Analysis of SRAM-Based FPGAs in High-Performance Information Systems

Soft errors due to cosmic particles are a growing reliability threat for VLSI systems. The vulnerability of FPGA-based designs to soft errors is higher than ASIC implementations since the majority of chip real estate is dedicated to memory bits, configuration bits, and user bits. Moreover, single event upsets (SEUs) in the configuration bits of SRAM-based FPGAs result in permanent errors in the mapped design. In this paper we analyze the soft error vulnerability of FPGAs used in information systems. Since the reliability requirements of these high performance information subsystems are very stringent, the reliability of the FPGA chips used in the design of such systems plays a critical role in overall system reliability. We present an analytical approach (versus fault injection) for soft error rate estimation in FPGA-based designs. We also validate the projections produced by our analytical model using field error rates obtained from failure data obtained from a large FPGA-based design used in the logical unit module board of a commercial information system. This comparison confirms that the projections obtained from our analytical tool are accurate (there is an 81% overlap in FIT rate range obtained with our analytical modeling framework and the field failure data studied).

Multi-user adaptive orthogonal frequency-division multiplexing system for indoor wireless optical communications

An adaptive orthogonal frequency-division multiplexing (OFDM) system is proposed for multi-user communications over indoor wireless optical channels. The designed system uses multi-user least-squares detection techniques applied to space-division multiple access and OFDM schemes, in conjunction with angle-diversity reception. The system, which does not present an excessive increase in complexity with respect to the previous schemes, can support high bit rates for multiple users, beyond 100 Mbits/s. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with that of a non-adaptive multi-user system and an adaptive single-user system, both described in the previous works, when they face similar environmental situations. The obtained results show a significant enhancement with respect to both the previous multi-user system and the adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment.

Chip-interleaved self-encoded multiple access with iterative detection in fading channels

We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels.