Uplink Bit Research Articles

Next generation earth-to-space telecommand coding and synchronization: ground system design, optimization and software implementation

The Consultative Committee for Space Data Systems, followed by all national and international space agencies, has updated the Telecommand Coding and Synchronization sublayer to introduce new powerful low-density parity-check (LDPC) codes. Their large coding gains significantly improve the system performance and allow new Telecommand services and profiles with higher bit rates and volumes. In this paper, we focus on the Telecommand transmitter implementation in the Ground Station baseband segment. First, we discuss the most important blocks and we focus on the most critical one, i.e., the LDPC encoder. We present and analyze two techniques, one based on a Shift Register Adder Accumulator and the other on Winograd convolution both exploiting the block circulant nature of the LDPC matrix. We show that these techniques provide a significant complexity reduction with respect to the usual encoder mapping, thus allowing to obtain high uplink bit rates. We then discuss the choice of a proper hardware or software platform, and we show that a Central Processing Unit-based software solution is able to achieve the high bit rates requested by the new Telecommand applications. Finally, we present the results of a set of tests on the real-time software implementation of the new system, comparing the performance achievable with the different encoding options.

A Package-Cognizant CMOS On-Chip Antenna for 2.4 GHz Free-Space and Implantable Applications

A 2.4 GHz industrial, scientific, and medical band on-chip antenna (OCA) is integrated into an on-chip broadband balun in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.18~\mu \text{m}$ </tex-math></inline-formula> CMOS technology on a die of size 4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Antenna miniaturization is achieved from the capacitive loading of meandered dipole arms. A back-to-back configuration of the balun on a separate die is characterized with in-band insertion and return loss of better than 0.9 dB and 20 dB, respectively. A commercial low-cost package is used to provide a decoupling effect to the OCA when immersed in tissue, enabling it to maintain stable impedance matching as in the air. A detailed explanation of the decoupling mechanism is provided using field plots and equivalent circuit analysis. The OCA is characterized in air and different tissue phantoms with a gain of −23.8 dBi in air and −25.9 dBi inside skin mimicking gel. The maximum simulated uplink specific absorption rate is obtained as 160 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> /kg for an input power of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~\mu \text{W}$ </tex-math></inline-formula> to the OCA in the transmitting mode. As the antenna has a small footprint and is analytically estimated to be capable of communicating at a high uplink bit rate of 1 Mb/s over a distance of 5.2 m with a 3 dB link margin, it is most suited as a minimally invasive implantable medical device.

Performance of an OFDM STBC-MISO system in uplink terrestrial-satellite laser communication.

We propose a space-time block coded multiple input single output (STBC-MISO) terrestrial-satellite laser communication uplink system based on orthogonal frequency division multiplexing (OFDM) modulation. It further uses Málaga distribution to simulate near-ground turbulence. Considering the combined effects of the uplink light intensity scintillation, beam wander, and angle-of-arrival fluctuation, a closed expression of the terrestrial-satellite uplink bit error rate for the proposed system is derived. The simulation analyzes the influence of transmitting radius, receiving aperture, beam divergence, zenith angle, and signal-to-noise ratio on the system's error performance, and compares it with OFDM modulated single input single output (SISO) and differential phase-shift keying-modulated SISO schemes. Finally, the experimental data are verified by the Monte Carlo method. This research provides a theoretical basis for research on MISO terrestrial-satellite laser communication uplink system coding technology.

A Spectrally Efficient Uplink Transmission Scheme Exploiting Similarity Among Short Bit Blocks

Next-generation cellular systems are anticipated to support 100 times higher data rates (ultra-high rate) compared with the fourth generation (4G) of cellular systems. It is, therefore, necessary to develop novel spectrally efficient uplink/downlink techniques. Multiple techniques have been proposed, including the so-called non-orthogonal multiple access (NOMA) technique. However, the spectral efficiency gains achieved by NOMA over OMA techniques have been shown to be modest. Recently, we proposed a spectrally efficient technique for the downlink channel, which involves exploiting similarities among users’ short bit blocks, where we showed that spectral efficiency gains of up to three times that of OMA schemes can be achieved. However, the technique cannot be extended to the uplink scenario because users are not aware of each other’s bit block. To this end, we propose in this paper a spectrally efficient scheme for the uplink channel, where we exploit the similarity between the short bit blocks of the uplink and downlink sequences corresponding to one user. The downlink bit sequences are those received by a user from the base station (BS). It is assumed that the BS keeps track of the bit sequences transmitted on the downlink channel to different users. The uplink and downlink bit sequences, which are assumed to be uncorrelated, are divided into bit blocks of short lengths, and then, the similarity between those blocks is extracted. Once each user determines its similarity index (i.e., the number of similar bit blocks) between its own bit sequence and its respective downlink bit sequence, this information is communicated with the BS, which will, in turn, select the user with the largest similarity index to transmit during that resource block. The same process repeats every resource block where the user with the maximum similarity index is always selected. We propose a simple overhead exchange algorithm that facilitates the exchange of the information on the similarity indexes between the users and the BS, where we assume that this exchange of information is done through a control channel. The performance of the proposed scheme and the overhead exchange algorithm is investigated analytically and by Monte Carlo simulations. Among the parameters that we incorporate into the analysis are the user density, the length of bit blocks used to check the similarity index, and the channel correlation. We show that spectral efficiency gains of approximately two times that of OMA schemes can be achieved.

Mean Bit Error Rate Evaluation of MC-CDMA Cellular Systems Employing Multiuser-Maximum-Likelihood Detector

In this paper, we evaluate the uplink bit error rate (BER) of multicarrier-code-division-multiple-access (MC-CDMA) cellular systems with multiuser-maximum-likelihood detector (MU-MLD). The scenario considers perfect power control, own-cell interference (or multiple access interference—MAI), interference from co-cells (or co-cell interference—CCI), additive white Gaussian noise, exponential path-loss and slow frequency-selective Rayleigh fading. Upper bound expressions to evaluate the mean BER are obtained, which are functions of the signal-to-noise ratio (SNR), the number of users, the spreading factor, and the channel reuse factor. For BPSK and 4-QAM (quadrature amplitude modulation), closed-form expressions involving the analytical calculation of pairwise error probabilities are obtained. For 16-QAM and 64-QAM, we show that the number of pairwise error probabilities needed to obtain the BER can be simplified through the constellations symmetry. The procedure for obtaining this simplification is detailed. Also, by considering BER asymptotes, expressions for the SNR penalty due to MAI are derived. Monte Carlo simulations verify the analytical expressions accuracy. In the simulations, the MU-MLD is implemented through the sphere decoder algorithm with MMSE QR factorization. Results show that MC-CDMA does not lose diversity due to MAI. Moreover, CCI significantly affects the system performance. As a consequence, it produces floors in the BER curves.

N2N Traffic Congestion Control for Wireless Coverage Sensor Networks

The performance of Node-to-Node (N2N) media streaming under Wireless Coverage Sensor Networks (WCSNs) depends on congestion control reducing the sink node load. This paper proposes a new Fuzzy Logic-based N2N Traffic Congestion Control (FL-NTCC) mechanism, to efficiently control traffic congestion in wireless coverage sensor networks. The proposed FL-NTCC congestion control mechanism is an efficient strategy that enhances the routing throughput for sensor nodes, and reduces traffic congestion and the uplink bit error rate in WCSNs. The proposed mechanism uses the Fuzzy Relevance Coefficient (FRC) μ, to control N2N traffic congestion in WCSNs. The simulation results show that in comparison with the other existing mechanisms, the proposed mechanism offers better performance.

Uplink bit combining for multiple base‐stations MIMO with applications to CoMP systems

AbstractThis work considers a simple bit level combining technique, aided by robust bit reliability information, for uplink collaborating multiple‐input multiple‐output (MIMO) base‐stations (also known as macrodiversity MIMO), operating over composite Rayleigh‐lognormal fading channels. Bit reliability weights based on a robust modification of the logarithmic likelihood ratio, combined with instantaneous symbol signal‐to‐noise ratio information, are derived for different local MIMO detection schemes. This bit reliability information is used at the fusion center, together with locally detected data, for combining and producing final information bits delivered to the destination. Computer simulation results confirm that such bit level combining techniques, when used with minimum mean squared error ordered successive interference cancelation and also with sphere decoding maximum likelihood local detectors, provide significant performance improvements over non‐collaborative base‐stations systems. Performance gains are maintained even when these schemes suffer from channel estimation errors and also in the presence of space correlation. Low backhaul overhead and performance advantages make these bit level combining techniques attractive for applications in next generation cellular systems employing coordinated multi‐point (CoMP) technology, as well as for other collaborative MIMO communication schemes.Copyright © 2014 John Wiley &amp; Sons, Ltd.

Coded QAM Backscatter Modulation for RFID

Radio Frequency Identification (RFID) systems, presently standardized under EPC Global Class-1 Gen-2, have attracted increasing interest as the next-generation technology for tagged object identification. One of the important objectives of this work is to highlight the fact that the performance of the backscatter uplink (determined by constellation choice and forward error correction) is coupled to the downlink via the power harvesting functionality. The concept of normalized power loss per bit is introduced for such RFID communication systems to capture the consequent trade-offs, that form the crux of the results. We explore the use of higher dimensional (4-QAM) modulation schemes in future RFID systems (beyond current binary modulation in Class-1 Gen 2) as a means to improve uplink bit rate. However, this results in significantly increased normalized power loss vis-a-vis 2-PSK, suggesting a role for FEC coding. New coded modulation schemes - based on unequal error protection - are proposed that provides additional degrees of freedom (via choice of code parameters) to trade-off spectral efficiency with normalized power loss. This is explored and quantified, resulting in design recommendations.

Interference Rejection Combining in LTE Networks

Long Term Evolution (LTE) provides high spectral efficiency within one cell, but it is shown to be highly vulnerable to inter-cell interference. While LTE as well as Wideband Code Division Multiple Access (WCDMA) suffers uplink interference especially with a frequency reuse factor of one, WCDMA has some inherent layer 1 mechanisms to alleviate these effects, namely macro-diversity and spreading codes. In contrast, LTE user data are more localized in the time/frequency domain, calling for different mechanisms for interference reduction in the receiver. For the higher layers, techniques such as fractional power control or fractional frequency reuse can be used to mitigate the interference but are shown to be sub-optimal. For layer 1, interference rejection combining (IRC) is described as an efficient alternative to increase uplink bit rates in areas where cells overlap. IRC principles in the presence of radio fading channels are detailed, while strategies for both interference suppression and signal-to-interference-plus-noise ratio (SINR) maximization are considered. Taking a didactic approach, we compare multiple antenna receiver techniques (maximal ratio combining (MRC), IRC, multiple input multiple output (MIMO)), analyze the key factors of IRC efficiency (the number of receiving antennas and interferers, time synchronization, interference over thermal, and scheduling decisions), and provide link level performance comparisons. We also provide implementation considerations for integrating the IRC in the current eNodeB receiver. As the purpose of this paper is to give a basic level introduction to IRC applied to the LTE uplink and highlight the respective surroundings, the IRC approach will be covered rather intuitively by illustrations without a great deal of theoretical detail. © 2012 Alcatel-Lucent.

HSUPA Transport Network Congestion Control

The introduction of High Speed Uplink Packet Access (HSUPA) greatly improves achievable uplink bitrate but it presents new challenges to be solved in the WCDMA radio access network. In the transport network, bandwidth reservation for HSUPA is not efficient and TCP cannot efficiently resolve congestion because of lower layer retransmissions. This paper proposes an HSUPA transport network flow control algorithm that handles congestion situations efficiently and supports Quality of Service differentiation. In the Radio Network Controller (RNC), transport network congestion is detected. Relying on the standardized control frame, the RNC notifies the Node B about transport network congestion. In case of transport network congestion, the Node B part of the HSUPA flow control instructs the air interface scheduler to reduce the bitrate of the flow to eliminate congestion. The performance analysis concentrates on transport network limited scenarios. It is shown that TCP cannot provide efficient congestion control. The proposed algorithm can achieve high end-user perceived throughput, while maintaining low delay, loss, and good fairness in the transport network.

Performance Analysis of Multicarrier DS-CDMA with Antenna Array in a Fading Channel

In this paper, an antenna array based base station receiver structure for multicarrier direct sequence code-division-multiple-access (Multicarrier DS-CDMA) system with binary phase shift keying (BPSK) modulation is proposed. One of the main advantages of the receiver structure is that the spatial diversity is obtained by combining signals at different array elements. Based on the detailed analysis of multiple access interference (MAI) and additive white Gaussian noise (AWGN) characteristics, the uplink bit error rate (BER) performance of the proposed antenna array Multicarrier DS-CDMA is provided. With regard to spatial domain combining, the optimum spatial combining (OSC) and suboptimum spatial combination (SOSC) weights is derived while the suboptimum set of weights is simplified in the sense that only the knowledge of array vector of desired user alone is sufficient for the combining. Simulation results verify the analysis, and it is shown that MAI is mitigated and subsequently the system performance is improved significantly by incorporating antenna array at the base station.

An overview of the KODEN experiment between the OICETS satellite and the optical ground station in NICT

The KODEN is a first in-orbit laser communication demonstration between a low earth orbit satellite called OICETS/Kirari and an optical ground station at the National Institute of Information and Communications Technology (NICT) in Koganei, Tokyo. Optical links could always be established even under atmospheric turbulence when partly clear skies were predominant in March, May, and September, 2006. The uplink and downlink bit error ratios were measured to be 10−7–10−3. This achievement is a milestone for future high-data-rate satellite communications.

Long-term statistics of laser beam propagation in an optical ground-to-geostationary satellite communications link

A ground-to-space laser communications experiment was conducted to verify the optical interfaces between a laser communications terminal in an optical ground station and an optical payload onboard a geostationary satellite 38 000 km away. The end-to-end optical characteristics such as intensity, sensitivity, wavelength, polarization, and the modulation scheme of optical signals as well as acquisition sequences of the terminals were tested under fairly good atmospheric conditions. The downlink's bit error rate was on the order of 10/sup -10/ in spite of atmospheric turbulence. Atmospheric turbulence-induced signal fading increased the uplink bit error rate, the best value of which was 2.5 /spl times/10/sup -5/ because the turbulent layer near the earth surface affects the uplink signal more than it does the downlink one. The far-field optical antenna patterns were measured through the ground-to-satellite laser links. The long-term statistics of the optical signal data is in good agreement with the calculated joint probability density function due to atmospheric turbulence and pointing jitter error effects, which means the stationary stochastic process can be applied to not only the static link analysis but also the dynamic link performance of the optical communications link. The equivalent broadened optical beam pattern should be used for the fading analysis even though the atmospheric coherence length is larger than the antenna diameter or the optical beam diameter of the transmitter. From these results, a more accurate dynamic link design of the optical communications link can be performed that would be useful for system designers, especially for designers of commercial systems.

Suppressing Opposite-Direction Interference in TDD/CDMA Systems With Asymmetric Traffic by Antenna Beamforming

One of the key advantages for the time-division duplex (TDD) system is the capability to deliver asymmetric traffic services by allocating different numbers of uplink and downlink time slots. However, in a TDD/code-division multiple-access (CDMA) system, asymmetric traffic may result in severe opposite-direction interference because downlink transmitted signals from neighboring base stations may interfere with the uplink received signals of the home cell. In this paper, we investigate the effect of four-antenna beamforming schemes from the perspective of suppressing the opposite-direction interference. We compare the uplink bit energy-to-interference density ratio of a traditional beam-steering technique (Scheme I) with that of the minimum-variance distortionless-response (MVDR) beamformer (Scheme II). Furthermore, Scheme III applies the conventional beam-steering technique for both downlink transmissions and the uplink reception. In Scheme IV, we implement beam-steering for downlink transmissions, while adopting the MVDR beamformer to process the uplink signals received at base stations. Our numerical results indicate that Scheme IV outperforms all the other three schemes, which can effectively suppress the strong opposite-direction interference in TDD/CDMA systems. While keeping low implementation costs in mind, employing the simpler Scheme III in a sectorized cellular system can also allow every cell to provide different rates of asymmetric traffic services.

On the use of a suppression filter for CDMA overlay

This paper is concerned with a direct-sequence code-division multiple-access (DS-CDMA) system operating over a Rayleigh fading channel and sharing a common spectrum with a narrow-band waveform. A suppression filter at the receiver is employed to reduce the narrow-band interference. We evaluate the average up-link bit error rate (BER) performance and investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter, the number of multiple-access users, the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth, the interference power to signal power ratio, the ratio of the offset of the interference carrier frequency from the spread-spectrum carrier frequency to the half spread-spectrum signal bandwidth, and so on.