Showing papers by "Barry G. Evans published in 2006"
TL;DR: An efficient algorithm is presented, which is superior in terms of frame/bit error rate performance and has approximately the same computational complexity as log-MAP decoding, exactly as for binary turbo codes.
Abstract: The constant log-MAP decoding algorithm suitable for duo-binary turbo codes. Motivated by an existing algorithm approach, an efficient algorithm is presented, which is superior in terms of frame/bit error rate performance and has approximately the same computational complexity. Compared with log-MAP decoding, the proposed algorithm has negligible performance degradation, exactly as for binary turbo codes.
21 citations
08 Dec 2006
TL;DR: In this paper, a cross-correlation based approach for improving timing estimation and frame detection performance in OFDM systems is proposed, which requires only one pilot symbol and can be used further for frequency offset estimation, by employing standard available techniques.
Abstract: A computationally simple cross-correlation based approach for improving timing estimation and frame detection performance in OFDM systems is proposed. The new technique requires only one pilot symbol and this can be used further for frequency-offset estimation, by employing standard available techniques. Simulation results show that the proposed approach performs more robustly relative to state-of-the-art autocorrelation based approaches. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
15 citations
11 Dec 2006
TL;DR: A novel 2-level channel multiplexing approach is proposed and developed that performs channel multipleXing at both transport and physical channels, and applies optimised 2-stage bin-packing algorithm for the channel mapping.
Abstract: Channel mapping is an important issue in the radio resource allocation scheme for the Satellite Digital Multimedia Broadcast (SDMB) system. Existing single-level channel multiplexing scheme performs well only when the bit rate of logical channel exactly matches the corresponding bit rate of the transport channel. In this paper, a novel 2-level channel multiplexing approach is proposed and developed. It performs channel multiplexing at both transport and physical channels, and applies optimised 2-stage bin-packing algorithm for the channel mapping. The results show that, in comparison with existing channel mapping schemes, our approach can require less number of transport channels, has better usage of the residual capacity on the transport channels, and can improve the total transmission capacity on the logical channels.
9 citations
08 Dec 2006
TL;DR: A novel packet scheduling scheme with a new power allocation algorithm has been proposed, and its performance has been evaluated via simulations, and the proposed strategy achieves significant performance improvement, especially on delay and jitter.
Abstract: The design of efficient radio resource management (RRM) is crucial for the multimedia content delivery in the satellite digital multimedia broadcasting (SDMB) system. In this paper, a novel packet scheduling scheme with a new power allocation algorithm has been proposed, and its performance has been evaluated via simulations. In comparison with existing schemes, the proposed strategy achieves significant performance improvement, especially on delay and jitter. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
7 citations
08 Dec 2006
TL;DR: In this article, the physical layer performance of HSDPA via GEO satellites for use in S-UMTS and SDMB was investigated and link-level results were presented on the performance of HARQ for a variable number of retransmissions and different categories of UE in a rich multipath urban environment with three IMRs.
Abstract: We investigate the physical layer performance of HSDPA via GEO satellites for use in S-UMTS and SDMB. The impact of large round trip delay on link adaptation is discussed and link-level results are presented on the performance of HARQ for a variable number of retransmissions and different categories of UE in a rich multipath urban environment with three IMRs. It is shown that the N-channel SAW HARQ protocol can significantly increase the average throughput particularly for 16-QAM but the large round trip delay also requires an increase in the number of parallel HARQ channels resulting in high memory requirements at the UE. Receive antenna diversity with varying degrees of antenna correlation is also investigated as a possible performance enhancing method. The results presented here will help in specifying the physical layer of satellite HSDPA. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
5 citations
01 Jan 2006
TL;DR: Analysis in this paper demonstrates that the use of cross-layer techniques could improve the performance of the targeted applications in terms of reduced delay while continuously maintaining an optimal speech coding rate for VoIP.
Abstract: Satellite communications can play an important role in extending the reach of broadband networks to terrestrially underserved areas. However, several popular internet applications could suffer from performance degradation over satellite (e.g. real-time gamming, web browsing, VoIP), thus necessitating protocol modifications and additional optimisation mechanisms. Cross-layer design, which is the optimisation technique adopted in this paper, is a relatively new idea in network design. It is based on blurred boundaries between network layers. In particular, two cross-layer mechanisms are described; the first adapts the VoIP speech coding rate according to network congestion while the second uses TCP state information at MAC layer in order to improve the throughput of TCP traffic. Analysis in this paper demonstrates that the use of cross-layer techniques could improve the performance of the targeted applications in terms of reduced delay while continuously maintaining an optimal speech coding rate for VoIP.
5 citations
08 Dec 2006
TL;DR: Simulation results are presented for assessing various aspects of the performance of the DVB -S2/RCS based satellite system in different mobile environments and the effects of different fading mechanisms on the Block Error Rate performance is analyzed through link -level simulations.
Abstract: Currently there is a clear trend towards vehicular satellite systems, which are designed in high frequency bands (Ku/Ka) and support broadband data services. One such system is designed within the European project MOWGLY for broadband services pro vision within aeronautical, maritime and railroad environments, and which features suitably adapted DVB -S2 and DVB -RCS standards as the basic underlying communications technology. This paper presents simulation results for assessing various aspects of the performance of the DVB -S2/RCS based satellite system in different mobile environments. In particular the effects of different fading mechanisms on the Block Error Rate performance of the system is analyzed through link -level simulations. Additionally , sys te m-level simulation results are provided that apart from complementing the link level simulations include the modeling of propagation impairments such as path loss and rain attenuation that cannot be captured in link level simulations.
4 citations
01 Oct 2006
TL;DR: A novel approach for improving the performance of the soft-output Viterbi algorithm (SOVA) when applied to turbo decoding is proposed based upon a modified two-step scaling factor approach for the decoder's extrinsic information.
Abstract: A novel approach for improving the performance of the soft-output Viterbi algorithm (SOVA) when applied to turbo decoding is proposed. Based upon a modified two-step scaling factor approach for the decoder's extrinsic information, it is shown that the proposed technique reduces significantly the error floor present in previous SOVA-based turbo decoding techniques. Various computer simulated bit error rate (BER) performance evaluation results for binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) and flat Rician fading channels clearly indicate that for large interleaver sizes and high numbers of decoding iterations no error floor is observed for BERs as low as 10 � 6 .
4 citations
TL;DR: This paper focuses on the two main reliable transport mechanisms in unidirectional, point-to-multipoint systems, namely packet-level forward error correction (FEC) and data carousels, and proposes design alternatives for both components as building components of an integrated scheme and investigates its performance via analytical means.
Abstract: One key aspect of digital multimedia broadcasting is the reliable point-to-multipoint distribution of content. Since the capacity and energy constraints in wireless environments do not favour the provision of a return channel for user feedback, the use of partial reliability techniques is often the only realistic option for the reliable transport layer design. In this paper, we focus on the two main reliable transport mechanisms in unidirectional, point-to-multipoint systems, namely packet-level forward error correction (FEC) and data carousels. We approach them as building components of an integrated scheme and investigate its performance via analytical means. Our analysis demonstrates that the network responsiveness, expressed by the average content access time, is optimized for certain packet-level FEC redundancy values. This is clearly different from setting FEC without considering the data carousel dimension, where the FEC redundancy is determined from the probability of recovering the whole file versus FEC overhead trade-off curves. We describe design alternatives for both scheme components, such as different FEC code types, rules for assigning FEC redundancy per carousel item, and ways to retrieve items from the data carousel, and evaluate their impact on the performance of the scheme. Our results suggest that the superposition of FEC on data carousels mitigates the otherwise significant impact of the data item retrieval technique on performance, at least for close-to-optimal FEC settings. On the contrary, the careful selection of FEC code and FEC redundancy assignment rule for data carousel items results in performance gains of up to 11 and 18% for the average content access time and FEC overhead, respectively, depending on the item demand and length distributions. Copyright © 2006 John Wiley & Sons, Ltd.
2 citations
08 Dec 2006
TL;DR: A system-level simulation analysis of MFTP performance in Inmarsat BGAN system in terms of transfer delay and system throughput as a function of available capacity, client population size, data product size, channel error characteristics, and MFTP protocol settings is presented.
Abstract: Their inherent broadcasting capabilities over very large geographical areas make satellite systems one of the most effective vehicles for multicast service delivery. Recent advances in spotbeam antennas and high-power platforms further accentuate the suitability of satellite systems as multicasting tools. The focus of this article is reliable multicast service delivery via geostationary satellite systems. Starburst MFTP is a feedback-based multicast transport protocol that is distinct from other such protocols in that it defers the retransmission of lost data until the end of the transmission of the complete data product. In contrast to other multicast transport protocols, MFTP retransmission strategy does not interrupt the fresh data transmission with the retransmissions of older segments. Thanks to this feature, receivers enjoying favourable channel conditions do not suffer from unnecessarily extended transfer delays due to those receivers that experience bad channel conditions. Existing research studies on MFTP's performance over satellite systems assume fixed-capacity satellite uplink channels dedicated to individual clients on the return link. Such fixed-assignment uplink access mechanisms are considered to be too wasteful uses of uplink resources for the sporadic and thin feedback traffic generated by MFTP clients. Indeed, such mechanisms may prematurely limit the scalability of MFTP as the multicast client population size grows. In contrast, the reference satellite system considered in this article employs demand-assignment multiple access (DAMA) with contention-based request signalling on the uplink. DAMA MAC (Medium Access Control) protocols in satellite systems are well-known in the literature for their improved resource utilisation and scalability features. Moreover, DAMA forms the basis for the uplink access mechanisms in prominent satellite networks such as Inmarsat's BGAN (Broadband Global Area Network), and return link specifications such as ETSI DVB-RCS, However, in comparison with fixed-assignment uplink access mechanisms, DAMA protocols may introduce unpredictable delays for MFTP feedback messages on the return link. Collisions among capacity requests on the contention channel, temporary lack of capacity on the reservation channel, and random transmission errors on the uplink are the potential causes of such delays, This article presents the results of a system-level simulation analysis of MFTP over a DAMA GEO satellite system with contention-based request channels. Inmarsat's BGAN system was selected as the reference architecture for analyses. The simulator implements the full interaction between the MFTP server and MFTP clients overlaid on top of the Inmarsat BGAN uplink access mechanism. The analyses aim to evaluate and optimise MFTP performance in Inmarsat BGAN system in terms of transfer delay and system throughput as a function of available capacity, client population size, data product size, channel error characteristics, and MFTP protocol settings. Copyright @ 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
2 citations
TL;DR: This paper focuses on some of the mechanisms which can provide partial reliability: the packet‐level forward error correction (PLFEC) technique in radio access network (RAN), different interleaving depths at physical layer (inter frame) and power allocation in the satellite radio interface.
Abstract: The inherent broadcast capabilities of satellites make them an attractive solution for the delivery of multimedia services to mobile users in third generation (3G) networks. Reliable delivery of content over a hostile land-mobile satellite channel is one of the key technical system requirements that can be addressed at different protocol layers. In this paper, we focus our attention on some of the mechanisms which can provide partial reliability: the packet-level forward error correction (PLFEC) technique in radio access network (RAN), different interleaving depths at physical layer (inter frame) and power allocation in the satellite radio interface. We rely on an end-to-end simulation platform in order to assess the performance gain achieved by these mechanisms separately, and provide clear indications for the achievable benefits at system level when some of these mechanisms act in co-ordination rather than in isolation.
11 Dec 2006
TL;DR: The feasibility of introducing a look-up table (LUT) based pre-distorter at the baseband of the gateway modem for linearizing the on-board traveling wave tube amplifier (TWTA) is studied.
Abstract: A very significant obstacle in employing Orthogonal Frequency Division Multiplexing (OFDM) in wideband satellite systems is its sensitivity to the non-linear response of the on-board Traveling wave Tube Amplifier (TWTA). Since satellite systems are power limited, backing-off the TWTA by a significant amount is not a realistic option. Therefore amplifier linearization techniques need to be employed in order to limit the impact of the non-linear signal distortions. This paper, studies the feasibility of introducing a Look-Up Table (LUT) based pre-distorter at the baseband of the gateway modem for linearizing the on-board TWTA. The LUT pre-distorter uses an adaptation algorithm for up-dating the table parameters according to the drifts in the amplifier's response over time and frequency. The study concentrates on evaluating the performance improvements that can be offered by the LUT pre-distorter, by making realistic assumptions regarding the training process, which in the satellite system needs to be based on the transmission of training sequences that propagate via an imperfect channel.
08 Dec 2006
TL;DR: In this article, simulation results are provided, which show that SC-FDE offers some improvements to conventional OFDM in a S-UMTS downlink in the context of satellite communications.
Abstract: Single Carrier Frequency Domain Equalization (SC-FDE), has recently attracted significant interest particularly in the wireless communications literature as an alternative air-interface solution to OFDM. Both SC-FDE and OFDM combat the detrimental effects of the frequency selective channel in a very efficient way; through the use of FFT/IFFT processing and parallel single-tap equalizers for each frequency bin. Despite their strong similarities, the two techniques differ in that in SC-FDE both the FFT and IFFT processing are performed at the receiving end. In the context of satellite communications, where power efficiency is a key objective, this difference translates into a much stronger resilience for SC-FDE to the non-linearity of the on-board High Power Amplifier (HPA). On the other hand the very high Peak-to-Average Power Ratio (PAPR) that characterizes OFDM signals requires employment of predistortion techniques and/or back-off. In this paper simulation results are provided, which show that SC-FDE offers some improvements to conventional OFDM in a S-UMTS downlink.