Transmit Power Spectral Density Research Articles

In-band full-duplex MIMO PLC systems for relaying networks

In Power Line Communications (PLC), there are regulatory masks that restrict the transmit power spectral density for electromagnetic compatibility reasons, which creates coverage issues despite the not too long distances. Hence, PLC networks often employ repeaters/relays, especially in smart grid neighborhood area networks. Even in broadband indoor PLC systems that offer a notable data rate, relaying may pave the way to new applications like being the backbone for wireless technologies in a cost-effective manner to support the Internet-of-things paradigm. In this paper, we study Multiple-Input Multiple-Output (MIMO) PLC systems that incorporate in-band full-duplex functionality in relaying networks. We present several MIMO configurations that allow end-to-end half-duplex or full-duplex operations and analyze the achievable performance with state-of-the-art PLC systems. To reach this analysis, we get channel realizations from random network layouts for indoor and outdoor scenarios. We adopt realistic MIMO channel and noise models and consider transmission techniques according to PLC standards. The concepts discussed in this work can be useful in the design of future PLC relay-aided networks for different applications that look for a coverage extension and/or throughput: smart grids with enhanced communications in outdoor scenarios, and “last meter” systems for high-speed connections everywhere in indoor ones.

Will OFDMA Improve the Performance of 802.11 Wifi Networks?

WiFi 6 based on the IEEE 802.11ax amendment is intended to improve spectral efficiency and area throughput operations in high density environments. This is achieved (among other methods) by the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) and enhanced multi-user Multiple Input Multiple Output (MU-MIMO) features. In this work, we explore the performance of downlink and uplink OFDMA in 802.11ax via extensive simulation based evaluation (latency, throughput, range) compared to conventional single user (SU) transmissions. Based on our results, we conclude that OFDMA can reduce the median latency from ~5 ms to less than 1 ms in non-saturation conditions. When used in conjunction with efficient multi-user buffer status report and restricted EDCA mechanisms, OFDMA can increase the saturation throughput by more than 10 percent. Moreover, UL OFDMA also improves aggregate throughput at longer ranges due to the narrower sub-channels (equivalently increased transmit power spectral density); four stations achieve an aggregate throughput 35 percent higher than a station transmitting SU frames and located at a range 1.5 times closer to the access point.

Modeling and Simulating on the Bandwidth and Capacity of Underwater Acoustic Channel

For underwater acoustic communication, the acoustic signals produce great attenuation in the propagation, and the complex environmental noise leads to the extremely limited bandwidth and capacity of the underwater acoustic channel. In this paper, the bandwidth and capacity of the channel are modeled and simulated under the condition that the transmitted power spectral density is constant. The theoretical analysis and simulation results show that the lower limit of the bandwidth of the underwater acoustic channel is determined by the noise and the upper limit is determined by the attenuation of the channel. Therefore, it is concluded that the narrow bandwidth of underwater acoustic channel is determined by attenuation and noise.

MIMO-OFDM NB-PLC Designs in Underground Medium-Voltage Networks

In this paper, we investigate the application of multi-input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) to narrowband powerline communications (NB-PLC) over medium-voltage (MV) underground (UG) networks. We study different MIMO transmission scenarios with different injection configurations utilizing both the cable conductor and sheath phases. Multiconductor transmission line theory is used to accurately characterize the UG MV NB-PLC channel transfer function and evaluate the spatial correlation between the different conductor phases. The achievable data rates are evaluated for all configurations at different line lengths after optimizing the transmit energy allocation across the different spatial information streams subject to a transmit power spectral density constraint. The achievable data rates for MIMO configurations are shown to be significantly higher (by up to three times higher) compared to single-input single-output OFDM transmission. Moreover, we investigate the effects of practical design constraints, such as cyclic prefix length and bit caps, on the achievable data rates. Finally, we show how to reduce the complexity of both the transmitter and receiver implementations while minimizing the data rate loss.

Spectral efficient pulse shape design for UWB communication with reduced ringing effect and performance evaluation for IEEE 802.15.4a channel

Ultra-Wideband (UWB) faces some regulations due to the interference issues with the co-existing narrowband communication systems, due to which the effective utilization of bandwidth is not possible that causes lower data rate of transmission. We propose a pulse shaping method which can curtail the interference with the co-existing band of communication and have an ability to depress the ringing oscillation. The modified pulse shape has an ability to control over the transmitted power spectral density and offers improved antenna power resolution. To obtain the specific results, the seventh derivative of Gaussian pulse is used as a basic pulse. This pulse is spectrally modified by windowing with Gaussian window to achieve the desired performance. The analysis is not only limited to spectral management but also inculcate the performance estimation of the resultant pulse in multi-user scenario for indoor multipath channel IEEE 802.15.4a. We have also analysed the modified pulse to prove its ability in the location accuracy improvement for high-end application of UWB communication.

Cooperative Impulse Radio Ultra-Wideband Communication Using Coherent and Non-Coherent Detectors: A Review

Ultra-wideband (UWB) is a booming technology in the field of wireless communication. This paper presents a brief idea related to the various coherent and non-coherent IR-UWB detectors. Due to the limitation in transmit power spectral density of UWB system, the major challenges faced by UWB system includes, achieving Quality of Service, system performance and coverage area. So, the combination of UWB system with cooperative communication will not only improve the system performance, but also help in expanding coverage area of signals. A brief review of the work done by various researchers in the field of cooperative impulse radio (IR) UWB communication is also presented in this paper. The working principle and performance analysis of the various coherent and non-coherent IR-UWB detectors using cooperative relay strategies are also discussed at large in this paper. The various fixed cooperative relay strategies used for cooperative UWB communication is Amplify and Forward, Decode and Forward and Detect and Forward. From the simulation results it can be inferred that, even though IR-UWB DTR receiver gives a much better BER performance than IR-UWB ED receiver using both cooperative and non-cooperative strategies, yet ED receiver is preferred because of its less complexity and low power consumption. Future prospects in the field of cooperative IR-UWB communication have also been discussed in this paper.

Ultra-wideband pulse shaping: bypassing the inherent limitations of the Gaussian monocycle

UWB impulse radio transmissions are power limited as they must respect a frequency mask with low total permitted power and severe isolation requirements for the GPS band. Shaping of the short UWB impulse maximizes transmit power subject to these constraints. We have previously published results for intricate pulse shaping in the optical domain that achieves record levels of power transmission. The most successful pulse shaping techniques in the electrical domain have been achieved with derivatives of the Gaussian pulse shape. The Gaussian monocycle is a low performance choice in terms of transmit power, but nonetheless the subject of intense research activity. In this paper we compare and contrast these UWB pulses, and quantitatively compare their performance in realistic systems (specific RF and antenna hardware). There is the perception that failings in the pulse shape (especially for the monocycle) can be compensated by simple highpass filter and the bandpass nature of the UWB antenna. We fabricate and characterize two UWB antenna designs available in the literature, as well as one commercial antenna. We use our optical pulse shaping device to experimentally investigate the three different pulse shapes and measure their transmitted power spectral density with each of the UWB antennas. We find that the monocycle is significantly less powerful than the others. The fine pulse shaping available in optical processing provides 1.7 to 2.9 dB gain over the electrical processing methods, depending on the antenna used.

Analytical results on channel capacity in uncompensated optical links with coherent detection

Based on a recently introduced model of non-linear propagation, we propose analytical formulas for the capacity limit of polarization-multiplexed ultra-dense WDM uncompensated coherent optical systems at the Nyquist limit, assuming both lumped and ideally distributed amplification. According to these formulas, capacity fundamentally depends on the transmitted power spectral density and on the total optical WDM bandwidth, whereas it does not depend on symbol-rate. Also, capacity approximately decreases by 2 [bit/s/Hz] for every doubling of link length. We show examples of capacity calculations for specific ultra-long-haul links with different polarization-multiplexed (PM) constellations, i.e. ideal PM-Gaussian, PM-QPSK (quadrature-phase shift keying) and PM-QAM (quadrature amplitude modulation). We show that the launch power maximizing capacity is independent of link length and modulation format. We also discuss the usable range of PM-QAM systems and validate analysis with simulations.

Improving cell edge throughput for LTE using combined uplink power control

Uplink power control is used in 3GPP Long Term Evolution (LTE) systems to maximize the power of the desired received signals while limiting the interference. This paper analyzes two power control mechanisms, Fractional Power Control (FPC) and Interference Based Power Control (IBPC). A way of combining them is proposed in order to find an efficient algorithm to control the transmitted Power Spectral Density (PSD) in order to compensate poor channel conditions and thus to obtain better performance in terms of cell edge throughput.

Design and Performance of Dual-Hop MIMO UWB Transmissions

To coexist with existing legacy wireless systems, the transmit power spectral density of ultrawideband (UWB) impulse radio systems is limited. The coverage range of UWB systems is then confined to within a few meters. Dual-hop relaying or multiple-input-multiple-output (MIMO) technology is one possible way of achieving greater UWB system coverage. This paper presents the design of dual-hop UWB MIMO relay systems (in which a source, relay, and destination have multiple antennas) according to the availability of channel state information (CSI) and their performance analysis over a UWB multipath fading channel. In particular, the decouple-and-forward and decode-and-forward relay systems are proposed when partial CSI is only available at the receiver side. On the other hand, with partial CSI being available at the transmitter side, we propose the amplify-and-forward and detect-and-forward relay systems. The exact formulas for the outage probabilities of those systems are derived. Furthermore, we evaluate, in closed form, the amount of fading and bit error rate expressions under sufficiently high signal-to-noise ratio and verify them through comparison with the simulation results. The effect of spatial correlation on the performance of our proposed systems is also studied. Numerical examples of the results provide valuable insights into the design of UWB MIMO relay systems.

Non-Coherent UWB Communications

Early UWB concepts for communications have almost exclusively relied on impulse radio, where the whole available bandwidth, i.e., up to 7.5 GHz, is covered at once by means of very short pulses which are generated with a low duty cycle. Meanwhile, a bandwidth of 7.5 GHz is only available in the US [1, 3]. In Europe, the spectrum which is available with the same transmit power spectral density of -41.3 dBm/MHz ranges only from 6.0 to 8.5 GHz [4], if no detect and avoid techniques are applied1. A potential UWB system has therefore to be able to ’live’ with a mean transmit power of less than -7.3 dBm.

Dynamic Spectrum Management: Complexity and Duality

Consider a communication system whereby multiple users share a common frequency band and must choose their transmit power spectral densities dynamically in response to physical channel conditions. Due to co-channel interference, the achievable data rate of each user depends on not only the power spectral density of its own, but also those of others in the system. Given any channel condition and assuming Gaussian signaling, we consider the problem to jointly determine all users' power spectral densities so as to maximize a system-wide utility function (e.g., weighted sum-rate of all users), subject to individual power constraints. For the discretized version of this nonconvex problem, we characterize its computational complexity by establishing the NP-hardness under various practical settings, and identify subclasses of the problem that are solvable in polynomial time. Moreover, we consider the Lagrangian dual relaxation of this nonconvex problem. Using the Lyapunov theorem in functional analysis, we rigorously prove a result first discovered by Yu and Lui (2006) that there is a zero duality gap for the continuous (Lebesgue integral) formulation. Moreover, we show that the duality gap for the discrete formulation vanishes asymptotically as the size of discretization decreases to zero.

Joint Signaling Techniques and Spectral Optimization for Symmetric Bit-Rate Communication Over Self-NEXT-Dominated Channels

We present a framework for maximizing the capacity of symmetric bit-rate communication services dominated by Gaussian crosstalk, in particular, digital subscriber line (DSL) services. We solve for optimal transmit power spectral densities (PSDs) that maximize the joint capacity of same-service users and yield significant gains in bit rates (or performance margins) over current schemes. Our results differ from previous work in that we develop transmit spectra in the presence of self-far-end crosstalk in addition to self-near-end crosstalk, present optimal contiguous spectra for practical modulation schemes, and derive optimal spectra under an additional frequency-domain peak-power constraint. Furthermore, by design, the optimal transmit PSDs are spectrally compatible with existing services on neighboring lines.

A CMOS ADSL codec for central office applications

A CMOS central office codec that supports Full Rate and G.Lite asymmetric digital subscriber line (ADSL) transmission is described. The transmit channel consists of application-dependent digital filters, a 14-bit, 8.832-MSample/s current steering DAC, a 1.104-MHz analog filter, and a programmable attenuator. Due to extensive on-chip digital signal processing, the codec complies with the ADSL transmit power spectral density standards without external filtering. The receive channel contains -17.5 to 33.5 dB of programmable gain staggered strategically across three stages, a 138-kHz analog low-pass filter, a 14-bit, 2.208-MSample/s pipeline ADC, and a digital 138-kHz low-pass filter. The receive channel has a wide input range that can accommodate large line voltages present at the line hybrid circuit. The IC occupies 55.2 mm/sup 2/ and dissipates 450 mW from a 3.3-V supply.

On the capacity of a twisted-wire pair: Gaussian model

The performance of a twisted-pair channel is assumed to be dominated by near-end crosstalk (NEXT) from other pairs in the same cable. Both intrabuilding local and central office loop channels can be modeled as NEXT-dominated channels. The capacity of this type of channel is found, using a Gaussian model. It is shown that the capacity is independent of the transmitted power spectral density. The results also indicate that present systems operate far below theoretical capacity. The capacity of a twisted-pair channel with both NEXT and white Gaussian noise present is also addressed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>