Adaptive Modulation and Coding

This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka-band multi-beam satellite system exploiting the new DVB-S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in-depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation-based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka-band multi-beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large-scale networks, are shown to perform very well, fulfilling the target packet-error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright © 2009 John Wiley & Sons, Ltd.

The demand for high-speed services and multimedia applications anywhere and anytime has led to the rise of wireless communications. In particular, WiMAX technology is nowadays considered one of the most prominent solutions capable to provide a Broadband Wireless Access ...

Scheduling amounts to allocating optimally channel, rate and power resources to multiple connections with diverse quality-of-service (QoS) requirements. It constitutes a throughput-critical task at the medium access control layer of today's wireless networks that has been tackled by seemingly unrelated information-theoretic and protocol design approaches. Capitalizing on convex optimization and stochastic approximation tools, the present paper develops a unified framework for channel-aware QoS-guaranteed scheduling protocols for use in adaptive wireless networks whereby multiple terminals are linked through orthogonal fading channels to an access point, and transmissions are (opportunistically) adjusted to the intended channel. The unification encompasses downlink and uplink with time-division or frequency-division duplex operation; full and quantized channel state information comprising a few bits communicated over a limited-rate feedback channel; different types of traffic (best effort, non-real-time, real-time); uniform and optimal power loading; off-line optimal scheduling schemes benchmarking fundamentally achievable rate limits; as well as on-line scheduling algorithms capable of dynamically learning the intended channel statistics and converging to the optimal benchmarks from any initial value. The take-home message offers an important cross-layer design guideline: judiciously developed, yet surprisingly simple, channel-adaptive, on-line schedulers can approach information-theoretic rate limits with QoS guarantees.

In anticipation of the high demand for wireless data services, several wireless standards are evolving to support packed data more efficiently. In UMTS, a new, shared channel called the high speed downlink shared channel (HS-DSCH) that multiplexes packet data users has been defined. Several performance-enhancing technologies are included in high speed downlink packet access (HSDPA): adaptive modulation and coding (AMC), hybrid ARQ (HARQ), scheduling etc. HARQ algorithm plays a critical role in HSDPA performance. HARQ techniques are classified in terms of the combining method (chase or incremental redundancy, IR), protocol timing (synchronous or asynchronous) and adaptivity (if modulation/code-rate can be changed for retransmission or not). In previous work (Das et al. 2001), an adaptive, asynchronous, incremental redundancy (A2IR) scheme was proposed and shown to provide substantial gains over other HARQ options. In this paper, the design and performance aspects of A2IR in the code domain (as against the time domain in Das et al.) are considered. Due to the higher bandwidth of the UMTS channels compared to cdma2000 or HDR, it is expected that code-division multiplexing (CDM) of users will be needed to "fill the data pipe" instead of pure time-division multiplexing. The paper also analyzes tradeoffs that are unique to implementing A2IR with CDM. A2IR with a fixed TTI is now part of UMTS Release 5.

Abstract In this paper, we proposed a neural network (NN) framework as a machine learning technique for link adaptation based on adaptive modulation and coding in 802.11 n MIMO-OFDM wireless system to predict the best modulation and coding scheme (MCS) index ...

Coupled with a robust and efficient OFDM air interface, MIMO technologies lead to a very compelling high-speed data downlink solution for future wireless systems. This article presents Nortel Networks' MIMO-OFDM concept prototype and measured performance results. This prototype has been developed in the framework of a Nortel Networks system concept for 3G evolution systems and next-generation wide area wireless networks.

This paper analyzes the efficiency of a joint-design of an adaptive modulation and coding (AMC) at the physical (PHY) layer with an adaptive R max-truncated selective-repeat automatic repeat request (ARQ) protocol at the medium access control (MAC) layer to maximize the throughput of cooperative non-regenerative relay networks under prescribed delay and/or error performance constraints. Particularly, we generalize the existing design model/results for cross-layer combining of AMC along with truncated ARQ in non-cooperative diversity networks in three-folds: (i) extension of the cross-layer PHY/MAC design or optimization to cooperative diversity systems; (ii) generalization/unification of analytical expressions for various network performance metrics to generalized block fading channels with independent but non-identically distributed (i.n.d) fading statistics among the spatially distributed nodes; (iii) analysis of the effectiveness of joint-adaptation of the maximum retransmission limit R max of ARQ protocol and cooperative diversity order N for delay-insensitive applications. Our insightful numerical results reveal that the average throughput can be increased significantly by judiciously combining two additional degrees of freedom (N and R max) that are available in cooperative amplify-and-forward (CAF) relay networks besides employing AMC at the PHY layer, especially in the most challenging low signal-to-noise ratio (SNR) regime. KEYWORDS cross-layer design, adaptive retransmission, cooperative relay diversity, adaptive modulation and coding 1. MOTIVATION It is well-known that the link adaptation techniques (e.g., adaptive modulation/coding) could dramatically enhance the spectral utilization efficiency of wireless networks that employ " fixed-transmission " methods. But to improve the transmission reliability/robustness at the physical (PHY) layer, one has to either increase the transmit power (thereby, decreasing the battery-life) or to reduce the transmission rate (e.g., by selecting a smaller constellation size or decreasing the code rate of forward error correction coding). Additionally, spatial/polarization diversity solutions at the physical layer (by employing multiple antenna elements at the transmitter and/or receiver) may not be reasonable on small-sized handheld portable devices or sensor nodes.

The TCP efficiency degradation in high delay- bandwidth product and error-prone channels is a well-known problem. To reduce this degradation, we utilized a hybrid wireless network architecture, where a geostationary bent-pipe satellite channel is used for forward high bit-rate transmissions, while the return link is realized through a terrestrial 3G segment. The performance of four of the most popular TCP versions are tested and compared via simulations in terms of goodput. Our aim is choosing which version performs better by using an Adaptive Coding and Modulation (ACM) technique, both alone and together with an Automatic Repeat reQuest (ARQ) scheme of the Selective Repeat (SR) type. ARQ is used with and without transmit and receive timeouts. The obtained results show that such a hybrid architecture is advantageous for TCP transmissions in terms of average goodput, and that ACM is effective only if used together with ARQ schemes.

In this paper, we propose a novel adaptive modulation and coding (AMC) algorithm dedicated to reduce the feedback frequency of the channel state information (CSI). There have been already plenty of works on AMC so as to exploit the bandwidth more efficiently with the CSI feedback to the transmitter. However, in some occasions, frequent CSI feedback is not favorable in these systems. This work considers finite-state Markov chain (FSMC) based channel prediction to alleviate the feedback while maximizing the overall throughput. We derive the close-form of the frame error rate (FER) based on channel prediction using limited CSI feedback. In addition, instead of switching settings according to the CSI, we also provide means to combine both CSI and FER as the switching parameter. Numerical results illustrate that the average throughput of the proposed algorithm has significant performance improvement over fixed modulation and coding while the CSI feedback being largely reduced.

Abstract—Code-division multiple-access (CDMA) has the po-tential to support traffic sources with a wide range of quality of service (QoS) requirements. The traffic carrying capacity of CDMA channels under QoS constraints (such as delay guarantee) is, however, less well-...

A prioritised adaptive CDMA scheme in which processing gain is given priority over modulation and coding schemes (MCS) in wireless systems is presented. The need for such design is necessary for increased bit rate. A scheme that has the capability to optimise both throughput and quality of service without sacrificing the required bit rate is designed. This is applied to

... 1,2 Cristiano Bonato Both, 1 Eliane Gobetti de Camargo, 1,3 Rafael Kunst, ... the Tx/Rx Transition Gap (TTG) and Rx/Tx Transmission Gap (RTG) are specified between the DL and UL subframes, and between UL and following DL subframe (in the next frame) to allow SS terminals ...