Abstract-In this paper, we develop solutions for the loading of digital subscriber loop (DSL) multicarrier (MC) systems that present constraints both on overall available energy and maximum energy per carrier. In the emerging G.DMT-based systems planned for high-throughput multimedia applications, the constraint on the peak-energy arises from spectral compatibility issues. However, until today, optimal solutions for loading peak-energy constrained MC systems do not seem explicitly developed in the literature. Hence, starting from suitable applications of the Kuhn-Tucker conditions, in this paper, we present the analytical relationships characterizing the optimal solution of the peak-energy-limited loading for the general case of concave "rate-functions," and then, we apply them in the context of the so-called "gap analysis." Thus, a low-complexity iterative algorithm implementing this solution is also developed, and its performance is numerically tested on several ANSI-standard asymmetric DSL (ADSL)-type loops impaired by crosstalk. Furthermore, a version of the presented loading algorithm that guarantees integer bit rates with low computational effort is also presented, and its performance is tested. The carried-out performance comparisons allow us to evaluate the throughput loss induced by peak-energy constraints in emerging ADSL-like services.Index Terms-ADSL, discrete multitone (DMT), greedy algorithm, Kuhn-Tucker conditions, MC modulation, NEXT/FEXT, peak-energy, quality of service (QoS), resource management, water filling. I. MOTIVATIONS AND GOALS OF THE WORKT HE INCREASING demand experienced over the past few years for interactive multimedia broadband residential services, such as high-speed Internet access and video on demand, presses the need to develop sophisticated asymmetric digital subscriber loop (ADSL) systems able to provide bit-rates exceeding 6 to 7 Mb/s over available twisted-pair copper wirings [9], [18]. Due to the requested high throughputs, the implementation of modems based on single-carrier modulation such as those developed in [25], [26] for high data rate DSL (HDSL) services seems too complex so that for these applications multicarrier (MC) modulation, such as discrete multitone (DMT), appears a more conservative Manuscript received July 26, 2001; revised January 30, 2002. The associate editor coordinating the review of this paper and approving it for publication was Prof. Vahid Tarokh.The authors are with INFOCOM Department, University of Rome "La Sapienza," Rome, Italy.Publisher Item Identifier S 1053-587X (02) for an extensive overview), nevertheless, none of them explicitly accounts for peak-energy constraints, and in any case, optimal solutions "ad-hoc" developed for loading peak-energy-limited MC systems do not seem available in the literature. Therefore, since the above algorithms typically account for constraints on the overall energy but neglect peak-energy limitations, their behavior on ADSL-type application scenarios is somewhat similar. In fact, they tend to gather most of ...
Abstract-Multiple-antennas constitute an effective mean to achieve spatial diversity in emerging bandwidth-efficient multiple-input multiple-output (MIMO) wireless systems. Until now, most contributions in this area are focused on the two limit cases of fully coherent and fully incoherent decoding, which, in turn, occur when perfect channel estimates and no channel estimates are available at the receiver. However, very accurate channel estimates typically demand long training sequences that reduces spectral efficiency. Therefore, testing capabilities of multiple-antenna systems with partially coherent decoding may be appealing for improving power-versus-bandwidth tradeoff. In this contribution, we focus on the optimized design and performance evaluations of multiple-antenna block-coded systems with partially-coherent maximum-likelihood (ML) decoding. After considering emerging fourth-generation WLANs (4GWLANs) as a possible application scenario, we present new performance bounds and optimized design criteria together with a new family of robust space-time unitary block codes that "self-match" to channel-estimation errors. We name these codes "self matching." Index Terms-Bandwidth-versus-power tradeoff, multiple-antenna, MIMO systems, partially coherent decoding, performance bounds, "self-matching" space-time block-codes, 4GWLAN.
Abstract. This paper deals with optimized Multiple-Input Multiple Output (MIMO) channel estimation and ensuing information throughput conveyed by pilot-based multi-antenna systems affected by both spatially colored Multiple Access Interference (MUI) and errors in the available channel estimates. The architecture of the Minimum Mean Square Error (MMSE) MIMO channel estimator is derived and the related analytical conditions for the optimal design of space-time training sequences are provided. Afterwards, closed form expressions for the maximum information throughput sustained by the considered systems for Gaussian distributed input signals are given and, then, a novel powers' allocation algorithm for the asymptotical achievement of the system capacity is developed. Considerations about optimized space-division MAC strategies are also provided.
Visible light communications seeks to leverage an unused medium for indoor wireless communications. A major goal is to deliver very high data-rates through LED luminaires to all places where we use lighting. However, the characteristics of LEDs and the nature of indoor lighting conspire to distort the signals. Illumination powers LEDs have low signaling bandwidth and exhibit severe frequency distortion. Their wide dispersion patterns, required for light and signal coverage, also add multipath distortion. Intermittent shadowing results in a wide range of channel characteristics. In this paper we address these challenges with an adaptive receiver. Namely, training is used to identify channel impairments, and our proposed receiver applies specific countermeasures including threshold detection, RAKE reception and adaptive channel equalization. Analysis and simulation demonstrate that our design mitigates distortion problems yielding a performance improvement of 40% to 100% with respect to the current literature in achievable bit-rate depending on the propagation scenario. © 2013 IEEE
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