Showing papers by "Barry G. Evans published in 2007"

Modified sum-product algorithms for decoding low-density parity-check codes

Abstract: The authors deal with the sum-product algorithm (SPA) based on the hyperbolic tangent (tanh) rule when it is applied for decoding low-density parity-check (LDPC) codes. Motivated by the finding that, because of the large number of multiplications required by the algorithm, an overflow in the decoder may occur, two novel modifications of the tanh function (and its inverse) are proposed. By means of computer simulations, both methods are evaluated using random-based LDPC codes with binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) channel. It is shown that the proposed modifications improve the bit error rate (BER) performance up to 1 dB with respect to the conventional SPA. These results have also shown that the error floor is removed at BER lower than 10 -6 . Furthermore, two novel approximations are presented to reduce the computational complexity of the tanh function (and its inverse), based on either a piecewise linear function or a quantisation table. It is shown that the proposed approximations can slightly improve the BER performance (up to 0.13 dB) in the former case, whereas small BER performance degradation is observed (<0.25 dB) in the latter case. In both cases, however, the decoding complexity is reduced significantly

SISO algorithms based on Max-Log-MAP and Log-MAP turbo decoding

Abstract: Novel soft-input soft-output (SISO) decoding algorithms suitable for turbo codes are proposed with good compromise between complexity and bit error rate (BER) performance. The algorithms are based on the application of the max/max* (i.e. Jacobian logarithm) operations at different levels when computing the decoder soft-output value. It is observed that some decoding schemes from the authors' previously published work fall into the family of methods described here. The effect is to provide a range of possibilities allowing system designers to make their own choices for turbo code BER performance against complexity.

A cross-layer packet scheduling scheme for multimedia broadcasting via satellite digital multimedia broadcasting system

Abstract: In recent years, multimedia content broadcasting via satellite has attracted increased attention. The satellite digital multimedia broadcasting (S-DMB) system has emerged as one of the most promising alternatives for the efficient delivery of multimedia broadcast multicast service (MBMS). The design of an efficient radio resource management (RRM) strategy, especially the packet scheduling scheme, becomes a key technique for provisioning multimedia services at required quality of service (QoS) in S-DMB. In this article, we propose a novel cross-layer packet scheduling scheme that consists of a combined delay and rate differentiation (CDRD) service prioritization algorithm and a dynamic rate matching (DRM)-based resource allocation algorithm. The proposed scheme considers multiple key factors that span from the application layer to the physical layer, aiming at simultaneously guaranteeing diverse QoS while utilizing radio resources efficiently under the system power and resource constraints. Simulation results demonstrate that the proposed cross-layer scheme achieves significantly better performance than existing schemes in queuing delay, jitter, and channel utilization.

Doppler spectrum of the multipath fading channel in mobile satellite systems with directional terminal antennas

Abstract: A new approach for determining the Doppler spectrum of narrowband multipath channels by assuming a three-dimensional propagation model is proposed. The new derivation methodology is first applied to determine the Doppler spectrum of a Rayleigh channel, when an omni-directional mobile-terminal antenna is assumed. The obtained results are shown to agree with the existing analytical results, which are available for particular assumptions regarding the angular distribution of the received multipath power. The main contribution is the derivation of the Doppler spectrum of the mobile satellite channel, where directive tracking terminal antennas are assumed. The results, which are dependent on the antenna's beamwidth and bearing, apply to emerging types of commercial vehicular satellite systems.

Comparison of SC-FDMA and HSUPA in the Return-Link of Evolved S-UMTS Architecture

Abstract: Single carrier frequency division multiple access (SC-FDMA), a multiple access technique similar to orthogonal frequency division multiple access (OFDMA), presently features as a strong candidate in the return link of the long time evolution (LTE) of T-UMTS. In the satellite domain there is an emerging research interest in extending mobile broadcasting system architectures that include complementary ground components, in providing bi-directional data services to mobile users. In such 'evolved S-UMTS' architecture, compatibility with current (CDMA based) and future (OFDMA/SC-FDMA) based) T-UMTS physical layer techniques is of high relevance, if satellite networks are to assume a complementary role to terrestrial ones. In this paper, we first give an overview of SC-FDMA and then compare, via simulations, the performance of the technique with that of the WCDMA-based high speed uplink packet access (HSUPA) that has been defined in release 6 of T-UMTS. The performance evaluations are performed over channels that are representative of the evolved S-UMTS architectures. Emphasis in the study is also given to realistic channel estimation and taking into account the effects of the amplifier's non-linearity. Other elements addressed in this paper are the impact of linearization techniques, and the pilot channel design in order to achieve robust estimation in the presence of non-linear channels.

A Cross-Layer Packet Scheduling Scheme for Multimedia Broadcasting via Satellite Digital Multimedia Broadcasting System [Advances in Mobile Multimedia]

Abstract: In recent years, multimedia content broadcasting via satellite has attracted increased attention. The satellite digital multimedia broadcasting (S-DMB) system has emerged as one of the most promising alternatives for the efficient delivery of multimedia broadcast multicast service (MBMS). The design of an efficient radio resource management (RRM) strategy, especially the packet scheduling scheme, becomes a key technique for provisioning multimedia services at required quality of service (QoS) in S-DMB. In this article, we propose a novel cross-layer packet scheduling scheme that consists of a combined delay and rate differentiation (CDRD) service prioritization algorithm and a dynamic rate matching (DRM)-based resource allocation algorithm. The proposed scheme considers multiple key factors that span from the application layer to the physical layer, aiming at simultaneously guaranteeing diverse QoS while utilizing radio resources efficiently under the system power and resource constraints. Simulation results demonstrate that the proposed cross-layer scheme achieves significantly better performance than existing schemes in queuing delay, jitter, and channel utilization.

Systems and Services

Abstract: After several science fiction papers and books, satellite telecommunications appeared with the paper titled “Extraterrestrial Relays” authored by Arthur Clarke and published on Wireless World in October 1945. In that paper, the orbital configuration of a satellite constellation utilizing a Geostationary Earth Orbit (GEO), an orbit located at 35800 km over the Earth surface coplanar with the equatorial plane, was proposed. In that configuration, three manned satellites, fixed with respect to a point on the Earth surface, were equally spaced in angle of 120° each and covered one third of the world. The second milestone was represented by the paper published in 1954, titled “Telecommunication Satellites”, authored by John Pierce where also Low Earth Orbit (LEO) were proposed using unmanned satellites. Latter, Highly Elliptical Orbit (HEO) and Medium Earth Orbit (MEO) have been considered.

A Cross-layer Approach for Packet Scheduling in Reliable Multicast Data Transmission over Geostationary Satellite Networks

Abstract: In this paper, we propose a channel-aware scheduling algorithm that exploits the reported channel state information (CSI) from all users in the multicast group for reliable transmission of multicast information over a geostationary satellite network. Reliability is guaranteed via a multicast transport protocol that retransmits lost segments to the multicast group. The proposed scheduling mechanism uses cross-layer CSI before making a decision whether or not a data segment is to be transmitted. As such, the algorithm avoids unfavourable channel conditions to reduce the forward link resources that would be wasted to retransmit lost segments. Scheduling delay and retransmission delay are found to be the elements of a trade-off, and simulations are conducted to attain optimal algorithm parameters to minimize session transfer delay in the face of L-band mobile channel conditions.

Combined Delay and Rate Differentiation Packet Scheduling for Multimedia Content Delivery in Satellite Broadcast/Multicast Systems

Abstract: The design of efficient packet scheduling algorithms is crucial to the radio resource management (RRM) in the satellite digital multimedia broadcasting (SDMB) system, which has emerged as a promising solution to the multimedia content delivery. In order to achieve more efficient quality of service (QoS) provisioning among different multimedia services, a novel packet scheduling algorithm, namely combined delay and rate differentiation (CDRD) packet scheduling, is proposed in this paper. This algorithm takes into account key QoS parameters aiming at fairly prioritising and scheduling heterogeneous multimedia contents in satellite environment. Its performance has been evaluated via simulations. The results show that, in comparison with existing scheduling algorithms, CDRD achieves better performance on delay, jitter and channel utilisation.

Aspects of Satellite Delivered Mobile TV (SDMB)

Abstract: In this paper we review satellite systems for radio and multimedia broadcast in the USA, Japan/Korea-Africa, Asia and the Middle East and in addition the various proposed systems for Europe. Many of these systems propose the use of the complimentary ground component (CGC) for urban/ indoor coverage. We address aspects of the original SDMB as well as the ETSI/SDR and DVB-SH variants recognising that there is significant synergy between them. This work was conducted as part of the SatNEx network of excellence.

Position-based DVB-RCS Spotbeam Handover in Vehicular Geostationary Satellite Networks

Abstract: High-speed Internet access is already a commodity in developed urban areas. We have also witnessed an increase in the number of airlines, railways, and maritime passengers that expect communication services while outside the coverage of terrestrial networks. Satellite systems are viewed as viable access providers for collective user communities on board aircraft, high-speed trains, and maritime vessels outside the coverage of terrestrial communication infrastructure. This article focuses on minimal mobility adaptations required by the ETSI DVB-RCS specification. First the performance of the existing DVB-RCS burst synchronisation is analysed in mobile vehicular networks. Then, a position-based seamless spotbeam handover mechanism is proposed, and its performance is analysed in terms of handover delay and handover failure rate using a ns-based packet-level simulator of DVB-RCS specification in a multi-spotbeam, multi-satellite geostationary constellation.

Feedback Implosion Suppression Algorithm for Reliable Multicast Data Transmission over Geostationary Satellite Networks

Abstract: In this paper, we propose a feedback implosion suppression (FIS) algorithm that reduces the volume of feedback traffic from receivers in a multicast group over a geostationary satellite network. The system considered in this paper includes a reliable multicast transport protocol that operates on top of a channel-aware scheduler (CAS) with receivers capable of measuring and feeding back to the scheduler their channel state information (CSI). The collected CSI becomes a valuable input to avoid unfavorable channel conditions to reduce the forward link resources that would be wasted to retransmit lost segments. Using a fixed number of available uplink slots, the Radio Network Controller (RNC) decides which receivers to update their feedback messages in the next collection period based on their CSI in the current cycle. The integration of FIS and CAS modules achieves a degree of full reliability in multicast transmission over a satellite network without relying on any collaboration between receivers, or on any infrastructure other than the satellite network.

Adaptive Multi-Dimensional QoS-Based Packet Scheduling Scheme for Multimedia Broadcasting Over Geostationary Satellite Networks

Abstract: Future success towards 3G and beyond systems is in supporting a variety of multimedia services with diverse quality-of-service (QoS) demands. With their inherent broadcast capabilities, the broadband satellite networks are regarded as a promising platform for delivering multimedia services. For these systems, it is highly desired that the available resources can be utilized in an optimized way. Packet scheduling schemes play a key role in providing various QoS support for provisioning multimedia services. By taking into account essential aspects of QoS provisioning whilst preserving the system power/resource constraints, the proposed Adaptive Multi-dimensional QoS-based (AMQ) packet scheduling scheme aims to effectively satisfy diverse QoS requirements and adaptively optimize the resource utilization for satellite multimedia broadcasting. Simulation results show that the AMQ achieves much better performance than those of existing schemes by satisfying multiple QoS aspects, such as delay, throughput, channel utilization and fairness.

DVB-RCS mobility management in vehicular satellite networks

Abstract: This article focuses on link and network-layer mobility issues in vehicular DVB-RCS satellite networks. The article presents a discussion on these topics before proposing a position-based spotbeam handover mechanism in some detail. The mechanism relies on regular position updates being available at mobile terminals. The NCC is responsible for making spotbeam handover decisions according to handover need information from mobile terminals with the objective to balance the load and maximise the overall utilisation. Particular emphasis has been placed on signalling issues. Backwardcompatible, light-weight, add-on mechanisms are crucial for commercial viability of a mobile DVB-RCS. Similarly, accurate modelling of existing DVB-RCS signalling mechanisms is necessary to attain useful conclusions regarding the performance of new handover mechanisms. The article briefly presents our ns-based DVB-RCS simulator and presents the performance analyses of our spotbeam handover mechanism in terms of failure rate and delay for. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Gradient Projection Decoding of LDPC Codes

Abstract: A new practical method for decoding low-density parity check (LDPC) codes is presented. The followed approach involves reformulating the parity check equations using nonlinear functions of a specific form, defined over Rrho, where rho denotes the check node degree. By constraining the inputs to these functions in the closed convex subset [0,1]rho ("box" set) of Rrho, and also by exploiting their form, a multimodal objective function that entails the code constraints is formulated. The gradient projection algorithm is then used for searching for a valid codeword that lies in the vicinity of the channel observation. The computational complexity of the new decoding technique is practically sub-linearly dependent on the code's length, while processing on each variable node can be performed in parallel allowing very low decoding latencies. Simulation results show that convergence is achieved within 10 iterations, although some performance degradations relative to the belief propagation (BP) algorithm are observed

Chip Level Adaptive Equalization for Satellite High Speed Downlink Packet Access (S-HSDPA)

Abstract: S-HSDPA is a concept that modifies terrestrial HSDPA in order to increase the throughput for S-UMTS and SDMB systems. In this paper, we consider S-HSDPA transmitted signals from GEO satellites via the IMR channel to the UE. The IMR channel is a highly dispersive multipath fading channel, and for this reason, the orthogonality between spreading signatures is lost, resulting in a reduction of average achievable throughput. In order to improve the performance, we investigate the performance of a linear chip level equalizer introduced at the receiver side. The results presented here highlight the advantage of the low complexity CPICH NLMS equalizer in comparison to a conventional RAKE receiver. The CPICH NLMS equalizer successfully increases the throughput of the SHSDPA by retaining the signal orthogonality with a relatively small increase in computational complexity.

A channel-aware scheduler with feedback implosion suppression in reliable multicast data transmission over geostationary satellite networks

Abstract: In this paper, we propose a channel-aware scheduling algorithm and feedback implosion suppression (FIS) technique that exploits reported Channel State Information (CSI) through the return link from a subset of users in a multicast group for reliable multicast delivery over a geostationary satellite network. Reliability is guaranteed via a MFTP-like transport protocol that retransmits lost segments to the group. The deployed scheduling mechanism uses CSI collected from group members before making a decision as to whether or not to transmit a data segment in the forward link. As such, the algorithm aims at avoiding unfavourable channel conditions to reduce the forward link resources that would be wasted in retransmission. However, the users' feedback collected from a large pool would result in the feedback implosion problem. Hence, we propose a FIS technique to complement the CSI collection policy to reduce traffic implosion in the return link as well as reducing the probability to transmit unnecessary CSI values. A change detection scheme run at the users' terminal is implemented using rectangular sliding test window to update a smoothed CSI value depending on its discrepancies with a nominal model from a reference window. The scheduling algorithm together with the CSI collection and FIS policies aims to reduce file transfer delay (FTD) by trading off total number of CSI updates in the face of L-band mobile satellite channel conditions. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Adaptive coding and modulation for vehicular satellite communications

Abstract: This paper presents the findings of an effort to establish the performance of ACM as defined in the DVB-S2 standard, in the context of vehicular satellite communications. The effects of multipath fading as well as rain attenuation and the high round trip delays associated with geostationary satellite systems are discussed. Performance results have been obtained by means of link level simulations. The work has been curried out under the FP6 project MOWGLY whose objective is the design, testing and implementation of a prototype system for broadband satellite communications to aircraft, maritime vessels and high speed trains. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Low-Complexity Frequency Estimator for DVB-S2 and Burst Transmissions at Low SNR

Abstract: A simple method for frequency estimation of a PSK-modulated carrier in complex additive white Gaussian noise is proposed. Although this feedforward pilot-aided technique is sub-optimal in terms of the Cramer-Rao bound (CRB) for one pilot field, its performance greatly improves (in comparison to some established methods) when used over consecutive pilot fields. At low signal-to-noise ratios (SNR) where there is an inherent use of averaging over consecutive pilot fields to achieve the required estimation accuracy, this method achieves a similar speed and accuracy to Luise and Reggiannini (L&R)'s method for fine frequency recovery but with a significantly lower complexity. It also provides a competitive speed and accuracy for coarse frequency offset estimation without a threshold region as associated with Kay's method. Simulations have been run based on the DVB-S2 standard (with all examined methods benefiting from the averaging over multiple pilot fields) and the results are presented. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Providing Proportional Loss Differentiation over Bandwidth on Demand Satellite Networks

Abstract: Next generation Internet requires the capability of providing quality of service (QoS) with service differentiation. Broadband satellite networks as an integral part of the global broadband network infrastructure are moving towards the same goal of providing service differentiation. Due to the unique properties of the space environment, providing service differentiation in satellite networks has additional challenges such as long propagation delay. In this paper, we present an innovative profile-based probabilistic dropping scheme for the provision of relative loss differentiation in a geostationary (GEO) bandwidth on demand (BoD) satellite network which follows the DVB-RCS standard, approved and published by ETSI for interactive broadband satellite network. The network is structured to support a finite number of ordered service classes. We adopt the proportional differentiated service (PDS) model which strikes a balance between the strict QoS guarantee of Integrated Services (IntServ) and softer QoS guarantee of Differentiated Services (DiffServ) to provide proportional loss differentiation to different priority classes. Our scheme controls the loss rates by computing the appropriate packet drop probability based on the congestion level within each satellite terminal (ST) independent of operating condition of other terminals and without requiring a central controller or monitor. Unlike previous proposals designed for terrestrial and wireless networks where the correct differentiation is only achieved locally on per-hop basis (i.e. the queues for different classes must be co-located in a node sharing a common buffer and communication channel), our scheme is able to maintain network-wide proportional loss even though the queues are physically distributed. Additionally, in the design of our solution, we ensure simplicity of the algorithm to minimize overhead incurred in the satellite network and also intra- and inter-node differentiation consistency. We extend the ns-2 simulator with the BoD capability analogous to the DVB-RCS system in which STs first request for resources (i.e. time slots) and only start transmitting packets following the reception of burst time plan (BTP). We implement our loss differentiation algorithm and attach it to each ST. Simulation results show that the scheme is able to achieve the PDS model in a heterogeneous ST environment. Our results also suggest that the predictability property of the PDS model may be violated if the service provider configures the performance gaps between service classes to be too close. However, our scheme can fully achieve the controllability property of the model.

Network architecture and radio resource management for Satellite Digital Multimedia Broadcast system

Abstract: How to deliver rich multimedia content to mobile users in a resource-efficient manner is a great challenge to the communication society. The Satellite Digital Multimedia Broadcast (SDMB) system has emerged as a promising solution on the efficient delivery of the Multimedia Broadcast Multicast Service (MBMS) by implementing a satellite-based broadcast service to complement the 3G and beyond 3G terrestrial mobile cellular networks. The SDMB covers large parts of Europe by integrating both mobile networks and satellite networks. This paper presents a picture of the SDMB system focusing on Its interworking and Radio Resource Management (RRM) Refereeing of this contribution was handled by M. DeSanctis. Manuscript received March 9, 2006; revised June 21, 2006. Released for publication April 27, 2007. Authoras Current Address: L. Liang, L. Fan, H. Du, Z. Sun and B.G. Evans, CCSR, University of Surrey, Guildford, Surrey, GU2 7XW, UK; C. Sener and N. Chuberre, Alcatel Space, 12 rue de la Baume, 75008, Paris, France; M. Fitch, British Telecommunications, Public limited Company, BT, Exact (831), 81 Newgate Street, London ECIA 7AJ, UK; M. Cole, LogicalCMG UK Limited, 75 Hampstead Road, London, NW I ZPL, UK; T. Boivin, Alcatel CIT. 8 rue de la Baume, 75008, Paris, France; and E. Buniout, Motorola Semiconductor SAS, Avenue General Eisenhower, BPI1029, 31023 Toulouse. France. 0885/8985/07/ USA $25.00 Q02007 IEEE issues and solutions. It first presents an overview of the SDMB system; then the network architecture and interfaces for the interworking between the SDMB and the terrestrial network are specified. To support the interworking on the access layer, we define the SDMB access layer that closely follows the Wideband Code Division Multiple Access (WCDMA) alr interface in order to achieve maximum commonality with the Terrestrial Universal Mobile Telecommunications System (T-UMTS). A proposed radio resource allocation algorithm on the access layer leads to the optimisation of radio resources.

On-Board Linear Interference Cancellation Multiuser Detection for Uplink CDMA GEO Satellite Systems

Abstract: [] In this paper, various IC MUD schemes namely SIC, PIC and PPIC are investigated for on-board implementation of uplink CDMA GEO satellite systems. The IC MUD schemes offer low complexity since they utilize matched filtering principle to cancel the MAI. We investigate two-stage IC MUD comparison under 6-dB Rician fading channel for on-board implementation. The results indicate that a two-stage PPIC shows a significant improvement over the conventional PIC and can approach the two-stage SIC performance (that has the best performance, but incurs a relatively large delay in processing and requires users re-ordering accordingly to the received power levels). We also examine the impact of asynchronous transmission and different power distribution to the PPIC performance. The results show that PPIC is most suitable for on-board implementation in CDMA GEO satellite systems.

Cross-Layer Joint Priority Packet Scheduling Scheme for Multimedia QoS Provisioning in Satellite Broadcast/Multicast Systems

Abstract: The design of efficient radio resource management (RRM) strategy has become a key technique for the next-generation wireless systems to provision multimedia data services at appropriate QoS. In this paper, the authors propose a novel cross-layer joint priority (CLJP) packet scheduling scheme for QoS provisioning of multimedia traffic in satellite broadcast/multicast systems. The scheme considers both the application and transport layers' QoS requirements and RLC layer's queuing status into MAC layer packet scheduling decisions, aiming at guaranteeing diverse QoS demands and achieving efficient resource allocation subject to power/resource constraints. In comparison with existing schemes, the simulation results prove that the proposed scheme achieves better QoS and fairness, and enhances the throughput/channel utilisation. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Carrier Synchronization for DVB-S2 systems in a Rician mobile environment

Abstract: The second generation standard for Digital Video Broadcasting via Satellite (DVB-S2) which was designed for fixed terminals is being considered for the delivery of broadband services to mobile platforms (such as airplanes, ships and trains). In this paper, we investigate the existing frequency synchronization algorithms that were proposed for DVB-S2 fixed terminals, in the specified mobile environment. Based on the simulation results obtained, a new algorithm is proposed to enhance frequency synchronization performance for DVB-S2 in the mobile channel. © 2007 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Cross-layer design and assessment of TCP congestion control protocols over future broadband satellite systems

Abstract: Adaptation of TCP for satellite links has been the subject of many research studies in the last decade. In many such studies, Performance Enhancing Proxies (PEPs) and modified TCP congestion control algorithms have been reported to considerably improve TCP performance over satellite systems. In parallel to Transport layer developments, Link layer mechanisms as well as satellite hardware design are also evolving, providing more reliable transmission and higher capacity utilisation. Under the new light of these evolutions, this paper presents a simulation campaign, comparing the performance of different TCP variants over a satellite network using PEPs. The second contribution of this paper is the performance assessment of a novel TCP congestion control mechanism based on cross-layer design. Cross-layer adaptation is a relatively new idea in network design, based on the vertical integration of protocol layers. Simulation results for this mechanism demonstrate the strong relationship between the Transport and Link layers and illustrate the benefits of joint analysis and design. © 2007 by University of Surrey.

Air interface research activities within SatNEx, the European satellite communications Network of Excellence

Abstract: SatNEx has brought together 24 partners from European research organizations and academia to form a pan-European research network. A major objective of SatNEx is to rectify the fragmentation in satellite communications research by bringing together leading European academic research organizations in a durable way. The paper presents the organization of the Network of Excellence and the "Air Interface" research activities. © 2007 by Prof. Michel Bousquet.