As we move from 5G to 6G networks satellites will play an increasingly key part in providing coverage and resilience. Here we outline the timescales and some of the issues facing satellites in the 6G world.

This paper analyses the New Radio (NR) air interface waveforms and numerologies in the context of current activities and studies of 3GPP related to the feasibility and standardisation of necessary adaptations for the 5G NR to support integrated-satellite-terrestrial networks with low earth orbit (LEO) satellites. Frequency-localized orthogonal frequency division multiplexing (OFDM)-based candidate waveforms are recommended by 3GPP as the waveforms for the NR in order to preserve the advantages of OFDM as well as maintain backward compatibility. 5G New Radio enables diverse service support, efficient synchronization and channel adaptability using a multinumerology concept, which defines a family of parameters of the parent waveform, that are related to each other by scaling. The major design challenges in the LEO satellite scenario are power limited link budget and high Doppler effects which can be addressed by choosing waveforms with small peak to average power ratio (PAPR) and sub-carrier bandwidth adaptation respectively. Hence, the selection of the right waveform and numerology is of prime relevance for the proper adaptation of 5G NR for LEO satellite terrestrial integration. The performance evaluation of the new air interface waveforms, with different numerologies, are carried out under the effect of carrier frequency offset (CFO), multipath effects, non-linearity, phase noise and additive white Gaussian noise (AWGN).

The emerging 5G wireless networks will pose extreme requirements such as high throughput and low latency. Caching as a promising technology can effectively decrease latency and provide customized services based on group users behaviour (GUB). In this paper, we carry out the energy efficiency analysis in the cache-enabled hyper cellular networks (HCNs), where the macro cells and small cells (SCs) are deployed heterogeneously with the control and user plane (C/U) split. Benefiting from the assistance of macro cells, a novel access scheme is proposed according to both user interest and fairness of service, where the SCs can turn into semi- sleep mode. Expressions of coverage probability, throughput and energy efficiency (EE) are derived analytically as the functions of key parameters, including the cache ability, search radius and backhaul limitation. Numerical results show that the proposed scheme in HCNs can increase the network coverage probability by more than 200% compared with the single- tier networks. The network EE can be improved by 54% than the nearest access scheme, with larger research radius and higher SC cache capacity under lower traffic load. Our performance study provides insights into the efficient use of cache in the 5G software defined networking (SDN).

The demand for wider bandwidths has motivated the need for wireless systems to migrate to higher frequency bands. In line with this trend is an envisaged deployment of Ka-band (or mmWave) cellular infrastructure. Further, to improve the spectral efficiency, developing full-duplex radio transceivers is gaining momentum. In view of this move, the paper proposes the possibility of reusing the satellite feeder uplink band in the full-duplex small cells. The motivation for such a reuse is two-fold :(a) there is virtually no interference from the small cells to the incumbent in-orbit satellite receiver, and (b) directive feeder antennas, with possibly additional isolation and processing causing negligible interference to the small cells. The presented interference analysis clearly supports the proposed coexistence.

With the worldwide evolution of 4G generation and revolution in the information and communications technology(ICT) field to meet the exponential increase of mobile data traffic in the 2020 era, the hybrid satellite and terrestrial network based on the soft defined features is proposed from a perspective of 5G. In this paper, an end-to-end architecture of hybrid satellite and terrestrial network under the control and user Plane (C/U) split concept is studied and the performances are analysed based on stochastic geometry. The relationship between spectral efficiency (SE) and energy efficiency (EE) is investigated, taking consideration of overhead costs, transmission and circuit power, backhaul of gateway (GW), and density of small cells. Numerical results show that, by optimizing the key parameters, the hybrid satellite and terrestrial network can achieve nearly 90% EE gain with only 3% SE loss in relative dense networks, and achieve both higher EE and SE gain (20% and 5% respectively) in sparse networks toward the future 5G green communication networks.

Abstract This paper investigates the radio resource management (RRM) issues in a heterogeneous macro‐femto network. The objective of femto deployment is to improve coverage, capacity, and experienced quality of service of indoor users. The location and density of user‐deployed femtos is not knowna‐priori. This makes interference management crucial. In particular, with co‐channel allocation (to improve resource utilization efficiency), RRM becomes involved because of both cross‐layer and co‐layer interference. In this paper, we review the resource allocation strategies available in the literature for heterogeneous macro‐femto network. Then, we propose a self‐organized resource allocation (SO‐RA) scheme for an orthogonal frequency division multiple access based macro‐femto network to mitigate co‐layer interference in the downlink transmission. We compare its performance with the existing schemes like Reuse‐1, adaptive frequency reuse (AFR), and AFR with power control (one of our proposed modification to AFR approach) in terms of 10 percentile user throughput and fairness to femto users. The performance of AFR with power control scheme matches closely with Reuse‐1, while the SO‐RA scheme achieves improved throughput and fairness performance. SO‐RA scheme ensures minimum throughput guarantee to all femto users and exhibits better performance than the existing state‐of‐the‐art resource allocation schemes.Copyright © 2014 John Wiley & Sons, Ltd.

Broadband access by satellite in Ka band is currently constrained by spectrum availability. In this context, the EU FP7 project CoRaSat is examining the possible ways in which improved frequency utilization could be possible in Ka band via the use of cognitive mechanisms. A database approach utilizing spectrum scenarios between Fixed Satellite Services (FSS), Fixed Services (FS) and Broadcast Satellite Service (BSS) feeder links are considered. Interference in the downlink from BSS and FS are evaluated using real data bases and propagation models. Data base statistics for several EU countries are also evaluated. The importance of using correct terrain profiles and accurate propagation models is shown. For the case of the BSS interference to the FSS downlink it is demonstrated that for the UK an area of less than 2% is affected and thus the additional 400 MHz spectrum band (17.3 to 17.7 GHz) can be used by FSS over the majority of the country. The operational challenges of the database approach across the EU are also discussed.

Spectrum sensing is one of the key technologies to realize dynamic spectrum access in cognitive radio (CR). In this paper, a novel database-augmented spectrum sensing algorithm is proposed for a secondary access to the TV White Space (TVWS) spectrum. The proposed database-augmented sensing algorithm is based on an existing geo-location database approach for detecting incumbents like Digital Terrestrial Television (DTT) and Programme Making and Special Events (PMSE) users, but is combined with spectrum sensing to further improve the protection to these primary users (PUs). A closed-form expression of secondary users' (SUs) spectral efficiency is also derived for its opportunistic access of TVWS. By implementing previously developed power control based geo-location database and adaptive spectrum sensing algorithm, the proposed database-augmented sensing algorithm demonstrates a better spectrum efficiency for SUs, and better protection for incumbent PUs than the exiting stand-alone geo-location database model. Furthermore, we analyze the effect of the unregistered PMSE on the reliable use of the channel for SUs.

In the literature, the Gaussian input is assumed in power optimization algorithms. However, this assumption is unrealistic, whereas practical systems use Finite Symbol Alphabet (FSA) input, (e.g., M-QAM). In this paper, we consider the optimal power for joint interweave and underlay CR systems given FSA inputs. We formulated our problem as convex optimization and solved it through general convex optimization tools. We observed that the total SU transmit power is always less than the power budget and remains in interference limited region only over the considered distance range. Therefore, we re-derive optimal power with interference constraint only in order to reduce the complexity of the algorithm by solving it analytically. Numerical results reveal that, for the considered distance range, the transmit power saving and the rate gain with the proposed algorithm is in the range 16–92% and 7–34%, respectively, depending on the modulation scheme (i.e., BPSK, QPSK and 16-QAM) used.

This paper addresses the Smart Gateway diversity scheme to be employed in future High Throughput Satellite Systems (HTS) at Ka, Q/V bands or above. The availability of a network of N gateways is presented with P redundant and with N active multiplexed gateways. A new time switched architecture is compared with the more conventional frequency division system for the N-active scheme but retaining transparent satellite transponders. In addition, resource allocation algorithms are compared, end to end, which maximize the throughput and balance the traffic amongst the user beams for gateways links degraded by rain. The time switched gateway approach allows simplifies satellite payloads and reduced ground segment size and hence cost.

There is a need to develop energy-efficient adaptive systems for future telecommunication networks. While traffic varies at different times, the power consumption of the radio access network does not scale with it effectively. To make significant energy savings, a dynamic deployment approach is required to allow the system to operate in an energy-efficient mode with respect to traffic load. By deploying small base stations within the area of a conventional macro station, we are able to reduce energy consumption while maintaining QoS. This paper proposes an energy-efficient dynamic deployment architecture based on fuzzy-logic. The algorithm aids in the decision of the architecture layout deployment. Moreover, by implementing the proposed adaptive energy-efficient algorithm, the network gains flexibility that can increase coverage or throughput throughout the same network by adapting its operation to source its requirements better and change them when new requirements arise.

In Cognitive Radio (CR) systems, the data rate of the Secondary User (SU) can be maximized by optimizing the transmit power, given a threshold for the interference caused to the Primary User (PU). In conventional power optimization algorithms, the Gaussian input distribution is assumed, which is unrealistic, whereas the Finite Symbol Alphabet (FSA) input distribution, (i.e., M-QAM) is more applicable to practical systems. In this paper, we consider the power optimization problem in multiple input multiple output orthogonal frequency division multiplexing based CR systems given FSA inputs, and derive an optimal power allocation scheme by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power compared to its conventional counterpart. Furthermore, our proposed scheme achieves higher data rate compared to the Gaussian optimized power due to fewer number of subcarriers being nulled. The proposed optimal power algorithm is evaluated and compared with the conventional power allocation algorithms using Monte Carlo simulations. Numerical results reveal that, for distances between the SU transmitter and the PU receiver ranging between 50m to 85m, the transmit power saving with the proposed algorithm is in the range 13–90%, whereas the rate gain is in the range 5–31% depending on the modulation scheme (i.e., BPSK, QPSK and 16-QAM) used.

In the literature, optimal power allocation assuming Gaussian input has been evaluated in OFDM based Cognitive Radio (CR) systems to maximize the capacity of the secondary user while keeping the interference introduced to the primary user band within tolerable range. However, the Gaussian input assumption is not practical and Finite Symbol Alphabet (FSA) input distributions, i.e., M-QAM are used in practical systems. In this paper, we consider the power optimization problem under the condition of FSA inputs as used in practical systems, and derive an optimal power allocation strategy by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power in a CR system compared to its conventional counterpart, that assumes Gaussian input. In addition to extra allocated power, i.e., power wastage, the conventional power allocation scheme also causes nulling of more subcarriers, leading to reduced transmission rate, compared to the proposed scheme. The proposed optimal power algorithm is evaluated and compared with the conventional algorithm assuming Gaussian input through simulations. Numerical results reveal that for interference threshold values ranging between 1mW to 3mW, the transmit power saving with the proposed algorithm is in the range between 55-75%, 42-62% and 12-28%, whereas the rate gain is in the range between 16.8-12.4%, 13-11.8% and 3-5.8% for BPSK, QPSK and 16-QAM inputs, respectively.

This study investigates collaboration among neighbouring base stations for the downlink of multi‐carrier cellular networks, in the absence of a centralised control unit, which is a defining characteristic of future wireless networks. The authors propose a novel scheme for collaboration in resource allocation among a cluster of three neighbouring base stations. In this scheme, the results of an initial calculation are shared among neighbouring cells, then the scheduling decision is made locally and independently by each cell. This scheme does not require complex and iterative calculation. The information is exchanged only once during each scheduling epoch, which results in reduced overhead on the backhaul links. The scheme is implemented in a distributed manner. Simulation‐based performance analysis demonstrates effectiveness of the proposed collaborative resource allocation scheme among the neighbouring base stations for multi‐carrier systems, particularly for the users located near the cell edges.

The ability to reliably and autonomously identify unused frequency bands plays an extremely important role in cognitive radio networks. Relying on the spectrum sensing, ongoing licensed operation must not be compromised and the secondary spectrum usage efficiency should be maintained. Thus, it is critical to ensure that the confidence level of the estimated signal status satisfies the primary user's requirement, while keeping the delay and computational complexity to a minimum. This study provides a comprehensive comparison in terms of performance, reliability and complexity of standalone sensing schemes for various cognitive radio application areas. The authors first give some new results on reliability performance, and then evaluate the sensing time required to achieve the target performance. Finally, the authors compare the computational complexity of various sensing approaches by calculating the number of arithmetic operations required by each approach.

Collaboration among neighbouring eNBs in radio resource allocation, in the absence of a centralized control unit, is one of the challenges raised from the flat architecture suggested for the Long Term Evolution (LTE) networks. This paper investigates the system performance of a collaborative resource allocation scheme, in a scenario that consists of two tiers of collaborative Regions (CoR), and considers the gain achieved from the eNB collaboration and performance degradation due to the interference from neighbouring eNBs. Our results indicate that interference introduced from the cells outside the collaborating cluster can have significant impact on the system performance. However, Monte Carlo simulation based performance analysis demonstrates the effectiveness of collaborative resource allocation among adjacent eNBs for the LTE networks.

This paper presents a signal-to-noise ratio (SNR) estimation algorithm for advanced digital video broadcasting- return channel via satellite (DVB-RCS) systems using adaptive coding and modulation (ACM). Due to the absence of a repetitive pilot symbol structure, SNR estimation has to be performed using the fixed symbol preamble data. Moreover, sporadic nature of data traffic on the return link causes variation in interference level from slot to slot and, therefore, the estimation has to be done within one traffic slot duration. Hence, it becomes necessary to use a combination of data-aided and decision-directed (DD) algorithms so as to make use of traffic data. A non-data-aided estimator that was previously proposed by the authors for binary and quadrature phase shift keying schemes is extended to 8-PSK in a decision directed manner. The inherent bias of DD approach at low values of SNR is reduced by using a hybrid approach, that is, using the proposed estimator at moderate/high values of SNR and the moments-based estimator (M2M4) at low values of SNR. Overall improved performance of the proposed hybrid estimator, in terms of accuracy and complexity, makes it an attractive choice for implementing ACM in advanced DVB-RCS systems.

In the context of orthogonal frequency division multiplexing (OFDM)-based systems, pilot-based beamforming (BF) exhibits a high degree of sensitivity to the pilot sub-carriers. Increasing the number of reference pilots significantly improves BF performance as well as system performance. However, this increase comes at the cost of data throughput, which inevitably shrinks due to transmission of additional pilots. Hence an approach where reference signals available to the BF process can be increased without transmitting additional pilots can exhibit superior system performance without compromising throughput. Thus, the authors present a novel three-stage iterative turbo beamforming (ITBF) algorithm for an OFDM-based hybrid terrestrial-satellite mobile system, which utilises both pilots and data to perform interference mitigation. Data sub-carriers are utilised as virtual reference signals in the BF process. Results show that when compared to non-iterative conventional BF, the proposed ITBF exhibits bit error rate gain of up to 2.5 dB with only one iteration.

Using multiple antennas in coexisting radio systems can cancel or control the co-channel interference and hence improves the overall spectrum efficiency. However, the hardware complexity and costs limit the usage of multiple-antenna technologies. Antenna selection technology may reduce such costs while partly remaining the advantages of the multiple-antenna technology. In this paper, the authors focus on the downlink of a multiple-input single-output (MISO) cognitive radio (CR) system and apply antenna selection techniques in the transmitter side of the secondary system. Two scenarios have been considered: one is single antenna selection and the other one is multiple antenna selection using linear beamforming. For the first scenario, the authors analyse the performance of minimum interference and maximum data power strategies, and then propose a maximum signal to leak interference power ratio (SLIR) strategy which consider both interference and useful signals; for the second scenario, the authors discuss the optimal, maximum norm, and proposed subset optimal strategy, which has lower computational complexity and less feedback information. Simulations results verified the analysis. It is also shown that the proposed methods achieve a better trade-off and obtain near-optimal performance in terms of SNR.

Adaptive interference mitigation requires significant resources due to recursive processing. Specific to satellite systems, interference mitigation by employing adaptive beamforming at the gateway or at the satellite both have associated problems. While ground based beamforming reduces the satellite payload complexity, it results in added feeder link bandwidth requirements, higher gateway complexity and suffers from feeder link channel degradations. On the other hand, employing adaptive beamforming onboard the satellite gives more flexibility in case of variation in traffic dynamics and also for changing of beam patterns. However, these advantages come at the cost of additional complexity at the satellite. In pursuit of retaining the benefits of onboard beamforming and to reduce the complexity associated with adaptive processing, we here propose a novel semi-adaptive beamformer for a Hybrid Terrestrial-Satellite Mobile System. The proposed algorithm is a dual form of beamforming that enables adaptive and non-adaptive processing to coexist via a robust gradient based switching mechanism. We present a detailed complexity analysis of the proposed algorithm and derive bounds associated with its power requirements. In the scenarios studied, results show that the proposed algorithm consumes up to 98% less filter computing power as compared to full-adaptive case without compromising on system performance.

Increasing concern about the energy consumption of cellular networks is driving operators to optimise energy utilisation without sacrificing user experience. In this paper, we consider the capability of spectrum sharing between two or more operators with the objective of achieving energy-efficient operation. Since each operator has a fixed amount of spectrum, they are required to increase the modulation index to achieve a higher data rate for a targeted QoS, which increases the demand on energy. We study the effect of using energy-efficient multilevel quadrature amplitude modulation (MQAM) with the capability of spectrum sharing between operators. Simulations show that using adaptive modulation with spectrum sharing between base stations of different operators can give a more flexible region for the system to operate with a reasonable trade-off.

This paper investigates collaboration among neighboring Base Stations (BSs) in OFDMA based cellular networks in the absence of a centralized control unit, which is a defining characteristic of 4G wireless networks. We propose a novel scheme for collaboration between the base stations. Monte Carlo simulation based performance analysis demonstrates effectiveness of collaborative resource allocation among adjacent base stations for OFDMA systems, particularly for the users in the cell edges.

This paper takes a broad view on the history and the present status of satellite communications and broadcasting. The necessary starting point of this overview is the visionary papers produced by Sir Arthur C. Clarke and John Pierce. This was the real dawn of the satellite communication era. This paper attempts to explain the “fil rouge” of the evolution of satellite technologies across six decades, analyzing successes and failures of past satellite missions, and concluding with a picture of future satellite communications.

This paper addresses mobile terminal (MT) relaying in order to improve the performance of mobile satellite broadcasting. It considers selective decode-and-forward (SDF) relaying with BICM-OFDM air interface. The BER upper bound was derived for the threshold-based SDF relaying in Rician fading channels. The suboptimal SNR threshold was then obtained by minimising this analytical upper bound. This scheme is compared in simulation with a conventional CRC and set threshold schemes. It is shown that the proposed suboptimal-SNR threshold scheme gives up to 1 dB performance gain compared to the conventional CRC-based scheme in the moderate Eb/Norange (i.e., 2 dBb/Nob/Noof 10 dB.

The current study proposes decoding algorithms for low density parity check codes (LDPC), which offer competitive performance-complexity trade-offs relative to some of the most efficient existing decoding techniques. Unlike existing low-complexity algorithms, which are essentially reduced complexity variations of the classical belief propagation algorithm, starting point in the developed algorithms is the gradient projections (GP) decoding technique, proposed by Kasparis and Evans (2007). The first part of this paper is concerned with the GP algorithm itself, and specifically with determining bounds on the step-size parameter, over which convergence is guaranteed. Consequently, the GP algorithm is reformulated as a message passing routine on a Tanner graph and this new formulation allows development of new low-complexity decoding routines. Simulation evaluations, performed mainly for geometry-based LDPC constructions, show that the new variations achieve similar performances and complexities per iteration to the state-of-the-art algorithms. However, the developed algorithms offer the implementation advantages that the memory-storage requirement is significantly reduced, and also that the performance and convergence speed can be finely traded-off by tuning the step-size parameter.

Some recently proposed robust methods for time domain timing and frequency synchronization in OFDM systems incorporate the use of cross-correlation based threshold detection in their timing adjustment and joint time-frequency algorithms. In this paper, we analyze the threshold criterion used and derive its theoretical performance. This translates into a better characterization of these OFDM synchronization algorithms, leading to a closer match between design expectations and practical performance. Computer simulations show a strong agreement between theoretical predictions and numerical results.

In this paper, we compare two multicast adaptive techniques for reliable data delivery in GEO satellite networks. Specifically, a channel-aware scheduling algorithm is compared with a multicast link adaptation technique, in the face of fluctuating channel conditions in downlink. The aim of the techniques is to maximise system throughput whilst increasing resource utilization. The scheduling technique is implemented within one forward bearer subtype, whereas the link adaptation mechanism considers transmission rates from a list of possible forward bearer subtypes. Simulation results are analysed and it is found that multicast link adaptation technique outperforms channel-aware scheduling algorithm, in terms of reduced session delay and retransmitted number of segments.

This paper investigates the connection between the classical sum-product (SP) decoder for low density parity check (LDPC) codes and the recently proposed gradient projection (GP) decoding scheme presented in (Kasparis and Evans, 2007). A graphical model for GP is exhibited based on which we derive an intermediate algorithm which establishes a bridge between graphical based algorithms (SP and variants) and an optimization based algorithm (GP). A more practical decoding algorithm with improved performance and reduced complexity is also proposed. A complexity analysis is provided and performance are studied through Monte-Carlo simulations.

In this paper, we propose a low complexity gradient based approach for enabling the Tone Reservation (TR) technique to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. The performance of the proposed algorithm is evaluated for different pilot location in the frequency domain, and also in combination with the discrete Fourier transform (DFT) spreading technique proposed in [Heung-Gyoon Ryu, et al., 2007]; in order to further reduce the PAPR. Simulation results show that the new technique achieves significant PAPR reductions, which are further enhanced when it is combined with DFT spreading. The simulation results also show that the performance of the technique is dependent on the pilot positions. In addition, further investigation was performed where the reduction tones are constrained, equal to the average power mask for the data tones, by a simple projection rule in the frequency domain both for the TR scheme and for the combined scheme. Simulation results show that the contiguous pilot arrangement provides better PAPR reduction performance in both cases, when the peak-cancellation signal is constrained in the frequency domain.

Satellites can complement terrestrial networks in Internet service provision by addressing the market which lies out of their reach. Despite of the global coverage, satellite networks entail high propagation delays and usually limited user bandwidth. VoIP is an example of an application which is subject to performance impairments due to these characteristics. VoIP trials over existing broadband satellite offers reveal that the application can be carried out with an acceptable quality. However results also reveal the need for further improvement of the bandwidth on demand scheme in order to reduce delay or improve bandwidth utilization. This paper presents a novel capacity request mechanism based on the accurate modeling of VoIP traffic as well as cross-layer design. Our analysis and simulation results show that our approach outperforms fixed capacity allocation mechanisms in terms of bandwidth efficiency or traditional bandwidth on demand schemes in terms of QoS.

The potential of an SNR estimation technique for use in links subject to multipath propagation and periodic shadowing is investigated. The proposed SNR estimator relies on the bit error rate of un-coded pilot sequences. The estimator's performance in the presence of Ricean fading, periodic shadowing and rain attenuation is analyzed by means of simulations. The proposed technique is shown to provide good estimation performance with reduced complexity compared to existing techniques.

With their inherent broadcast capacities and reliable extensive geographical coverage, the broadband satellite networks are emerged as a promising approach for the delivery of multimedia services in 3G and beyond systems. To utilise the available resources in an optimized way whilst guaranteeing the diverse quality-of-service (QoS) demands, an Adaptive QoS-aware Resource Allocation (AQRA) scheme is proposed in this paper for multimedia delivery in satellite broadcasting networks. By taking into account essential aspects of a successful QoS provisioning whilst preserving the system power/resource constraints, the proposed scheme is capable of allocating the resources, in an adaptive manner, according to the current QoS satisfaction of each session. Simulation results prove that the AQRA achieves significantly better performance than those of existing schemes on multiple performance metrics.

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.

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.

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.

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.

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.

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.

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.

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.

Multimedia Broadcast/Multicast Service (MBMS) is introduced in the Release 6 of the 3rdGeneration Partnership Project (3GPP) and is characterized by relatively longer interleaving depth. This paper investigates the exploitation of the longer interleaving depth by chip block interleaving to obtain intra-bit diversity. Both terrestrial and satellite modes of MBMS delivery mechanisms are studied and it is found out that chip block interleaving provides a reduction in the transmission power (2.5 dB in terrestrial flat Rayleigh fading channel, 0.75 dB in 4-tap 3GPP Case 3 radio channel, 1.5 dB in satellite line of sight Ricean flat fading channel and 0.7 dB in 9-tap satellite multipath fading due to intermediate module repeaters) at moderate speeds of 30-50 km/h and a moderate interleaving depth of 20 ms for 64 kbps data service. Moreover, it is also shown that for terrestrial mobile radio channels, the gain provided by chip block interleaving with block length equal to half the spreading factor and using only one transmit antenna is equal to that provided by Space Time Transmit Diversity (STTD) that requires two transmit antennas.

The paper addresses TCP performance enhancing proxy techniques broadly deployed in wireless networks. Drawing on available models for TCP latency, we describe an analytical model for the latency and the buffer requirements related to the split-TCP mechanism. Although the model applicability is broad, we present and evaluate the model in the context of geostationary satellite networks, where buffering requirements may become more dramatic. Simulation results are compared with the analytical model estimates and show that the model captures the impact of various parameters affecting the dynamics of the component connections traversing the terrestrial and the satellite network.

We investigate the use of fixed-point methods for predicting the performance of multiple TCP flows sharing geostationary satellite links. The problem formulation is general in that it can address both error-free and error-prone links, proxy mechanisms such as split-TCP connections and account for asymmetry and different satellite network configurations. We apply the method in the specific context of bandwidth on demand (BoD) satellite links. The analytical approximations show good agreement with simulation results, although they tend to be optimistic when the link is not saturated. The main constraint upon the method applicability is the limited availability of analytical models for the MAC-induced packet delay under non-homogeneous load and prioritization mechanisms.

It has long been a conjecture as to whether satellites have a role in mobile communications other than for niche areas such as sea and aero coverage. This paper attempts to answer this question by looking at the history of mobile satellite communications systems and the current developments towards multimedia, broadband, content and integrated systems. It projects into what is called the B3G era to show how satellites can play a useful role in cooperation with terrestrial systems.

Session initiation protocol (SIP) has been selected as the official end-to-end IP signalling protocol for establishing multimedia sessions in the IP-based universal mobile telecommunication systems (UMTS) network. Since a satellite component has been identified within UMTS, there is a need also to support SIP-based session establishment over satellite-UMTS (S-UMTS) to achieve an end-to-end seamless IP-based terrestrial/satellite network integration. To improve the session setup performance, a link layer retransmission based on the radio link control acknowledgement mode (RLC-AM) mechanisms is utilised. However the current RLC-AM procedure is found to be inefficient when applied to transactional-based applications such as session establishment. As such this paper proposes a scheme to alleviate this inefficiency and simulation results reveal that this scheme achieves a good compromise between delay and radio resource utilization under various channel conditions.

The elasticity of transmission control protocol (TCP) traffic complicates attempts to provide performance guarantees to TCP flows. The existence of different types of networks and environments on the connections' paths only aggravates this problem. In this paper, simulation is the primary means for investigating the specific problem in the context of bandwidth on demand (BoD) geostationary satellite networks. Proposed transport-layer options and mechanisms for TCP performance enhancement, studied in the single connection case or without taking into account the media access control (MAC)-shared nature of the satellite link, are evaluated within a BoD-aware satellite simulation environment. Available capabilities at MAC layer, enabling the provision of differentiated service to TCP flows, are demonstrated and the conditions under which they perform efficiently are investigated. The BoD scheduling algorithm and the policy regarding spare capacity distribution are two MAC-layer mechanisms that appear to be complementary in this context; the former is effective at high levels of traffic load, whereas the latter drives the differentiation at low traffic load. When coupled with transport layer mechanisms they can form distinct bearer services over the satellite network that increase the differentiation robustness against the TCP bias against connections with long round-trip times. We also explore the use of analytical, fixed-point methods to predict the performance at transport level and link level. The applicability of the approach is mainly limited by the lack of analytical models accounting for prioritization mechanisms at the MAC layer and the nonuniform distribution of traffic load among satellite terminals.

This paper reports a simulation study of the interaction between the transmission control protocol (TCP) and bandwidth on demand (BoD) mechanisms in broadband satellite networks. It forms part of a broader effort aiming at the identification of the proper mechanisms and algorithms to efficiently carry TCP traffic over these networks. We investigate two aspects of this rather complicated interaction, related to the possible BoD configurations and the TCP tuning parameters, focusing on GEO satellite networks. The impact on TCP performance and system efficiency is evaluated and effects that cannot be easily captured by analysis are highlighted.

In this paper we consider the effects of handover in LEO and MEO systems on data packet services. In particular, we investigate by simulation the application of packet communications to non GEO satellite networks, we discuss a MAC protocol for handover and non handover calls within a satellite footprint and simulate its performance for E-mail traffic.

Transmit power control is indispensable in direct sequence code division multiple access (DS/CDMA) based systems such as the Satellite Universal Mobile Telecommunication System (S-UMTS). The performance of fixed step-size closed loop power control is significantly affected by command delay due to processing and propagation. This calls for insights into the dynamics of transmit power control taking into account the effects of delays. In this paper, therefore, we have developed an analytical model for the dynamic behaviour of the error process as a stochastic difference equation. We have modelled the effects of delays in the presence of random external disturbances as a random walk process. Using the stochastic difference equation, we have developed an expression for the steady-state pdf of the power control error process as a lognormal distribution. However, we demonstrate that in cases where the quantisation errors of the power control command are significant, the error process departs from the lognormal distribution approximation. This shows that the generally assumed lognormal distribution for power control error process may not always be valid.

The random access channel (RACH) is an uplink shared channel for initial channel access to the network as well as for short data bursts. We propose modifications to the RACH preamble for satellite-UMTS using higher order of Hadamard codes, and it is shown that these enhancements have a better performance than that of the current Third Generation Partnership Project (3GPP) specifications and the European Telecommunications Standards Institute (ETSI) proposal.

User position information is an important factor for achieving efficient operation of global wireless networks. An accurate estimation of the mobile terminal (MT) location cannot be obtained if the radio signals are corrupted by noise or other sources of signal degradation. As a consequence, processing algorithms capable of generating a single point of interception from many noisy samples need to be implemented. Simulation results presented in this paper demonstrate that a simple and computational efficient recursive filtering technique is effective in reducing the uncertainty introduced by measurement noise in the user location estimate produced by CDMA-based dynamic satellite systems.

This paper presents a quantitative analysis by computer simulation of different handover algorithms for mobile satellite diversity based systems. The statistical but predefined nature of the constellation dynamics as well as the influence of the propagation channel in the handover mechanism enables the assessment of different levels of power and time hysteresis for different satellites within the network. Based on the above, two new handover algorithms are proposed for different modes of handover operation and compared with some known handover schemes by means of case studies in suburban environments for a LEO and a MEO satellite constellation.

A new strategy for iterative turbo decoding is proposed, where a class of symmetric Gaussian-like probability distributions are used to estimate the conditional probabilities of extrinsic values generated from branch detectors. A specific probability with a unique parameter is finally determined based on a proposed likelihood criterion of minimum estimated error bits for any detector in each iterative decoding. In this sense, the optimum distributions of the extrinsic values of iterative decoding are unveiled over AWGN, Rician and Rayleigh fading channels. The simulation results show that the decoding with this new technique has superior error performance to the traditional approach based on the conventional Gaussian law for the extrinsic values under the same channel conditions.

The objective of this paper is to analyse the impact of different handover strategies on the service quality and network efficiency of non-GEO satellite diversity based systems. To this end, a quantitative analysis by computer simulation of different handover algorithms for mobile satellite diversity based systems is presented. The statistical but predefined nature of the constellation dynamics as well as the influence of the propagation channel in the handover mechanism enables the assessment of different levels of power and time hysteresis for different satellites within the network. Based on the above, two handover algorithms are proposed for different modes of handover operation and compared with existing handover schemes by means of case studies in suburban environments for a LEO and a MEO satellite constellation. The analysis includes the simulation of the constellations and the elevation dependent satellite channel.

A new methodology for defining fixed location area in mobile satellite communication systems is proposed and its features are compared with the dynamic location area method in terms of implementation in the network and the mobile terminal.

An adaptive coding and modulation transmission scheme applicable for third-generation mobile satellite systems is proposed. The transmitter dynamically selects the optimum coding and modulation scheme according to the environment in order to maximize the spectrum and power efficiency. A constant average bit error rate (BER) is maintained without changing (or with a very small change to) the transmitted power, and hence the scheme eases the power control requirements. In addition, a higher throughput can be achieved compared to fixed (non-adaptive) systems. Unlike other adaptive transmission systems, in our work the adaptation is based on the Rice factor. The paper also discusses a Rice factor estimation algorithm.

This article presents a new method for the performance evaluation of concatenated coding schemes with inner convolutional code or trellis-coded modulation and outer Reed-Solomon code.

The Terminal at High Speed for European Stock Exchange USers (THESEUS) is a European research project. THESEUS with its multimedia communications capabilities enables brokers to trade not only with their national stock exchange but also with all the European stock exchanges. This will make secure trading in the stock exchanges more effective through Europe. This paper presents an overview of the THESEUS system design and architecture and the terrestrial, satellite and security field demonstrations.

The design of a satellite mobile multimedia communication system operating at Ka band and using synchronous CDMA is presented. The air interface described in the paper was derived taking into account the requirements induced by the provision of multimedia services to compact portable and mobile terminals. In order to minimize the complexity of the satellite payload, the concept of partial frequency reuse is introduced. A novel algorithm based on evolutionary theory is derived in order to optimize the corresponding link dimensioning. The satellite payload is described, and techniques reducing the computational requirements are proposed. It is then shown that the on-board complexity associated with the given design is within acceptable technological limits.

In this paper we analyse the performance of a medium access control (MAC) protocol which is particularly suited for a scenario with a high number of terminals with very bursty unspecified bit rate (UBR) traffic (e.g. web browsing). In order to guarantee the required quality of service (QoS) requested by the user for all ATM service classes, priorities between the service classes must be implemented. Hence prioritised queueing of requests is proposed. The adaptive MAC protocol was designed to allow statistical multiplexing of ATM traffic over the air interface, especially for independent and spatially distributed terminals. It is shown that the potential user population which can be served is considerably increased by statistically multiplexing bursty traffic over the air interface.

This paper evaluates the internetwork handover performance in a GSM and satellite integrated mobile communication system. The performance evaluation is based on an analytical model developed for internetwork handover. The handover performance parameters considered are the handover position, unnecessary handover probability, and call-dropping probability. Handover initiation is based on the signal level and distance measurement. The results are compared with those of the GSM handover performance. The analysis shows that the performance achieved in internetwork handover can be similar to those of the GSM handover with the considered handover initiation scheme.

We describe the main principles governing the ETSI-RES 10 HIPERLAN standard for the deployment of ad-hoc wireless local area networks. Focusing on the requirements for supporting delay sensitive services, we compare the performance of the multiple access method adopted in HIPERLAN (called EY-NPMA), to that of a dynamic TDMA access technique.

The demand for global telephony services for mobile users requires the use of constellations of non-geostationary orbits. The proposed S-PCNs are Iridium, Inmarsat-P, Globalstar, Odyssey and Ellipso. The first two systems propose to use a time division multiple access (TDMA) scheme and the others code division multiple access (CDMA) scheme. It is claimed that CDMA based S-PCNs can share the allocated frequency bands due to the interference resistant property of CDMA. Spectrum sharing must be based on defined interference criteria being satisfied. The interference events are based on the statistics of carrier to interference ratio (C/I). For this a computer simulation was developed to model the dynamic nature of any constellation, and produces all the statistical values of C/I to a mobile in a fading channel. The simulation includes constellations results of proposed S-PCNs with multi-spotbeam antennas (MBA). We present the results of the investigation on the effect of imperfect power control on the total system capacity for a totally overlapped band sharing scenario. Results for a band segmented scenario are also presented for comparison.

Call set-up delay is one of the important factors to assess the quality of service in communication networks. Due to the power limitation problem in satellite personal communication networks (S-PCN), channel fading effects will cause signalling errors. Hence ARQ techniques are required. In this paper we examine the data link layer protocol used on the dedicated control channels (DCCH) in GSM systems. Two alternatives, modified go-back-N (GBN) and selective re-transmission (SRT) ARQ protocols, are proposed for the DCCH at the satellite air-interface. The optimum window size is investigated through the trade-off between the call set-up delay and the signalling capacity requirement.

This paper derives the average bit error probability (BEP) for bandlimited hybrid SFH/DS-CDMA over an additive white Gaussian channel when overlapping of adjacent hopping bands is permitted in the frequency domain. The numerical results which focused on the gain by overlapping of the hopping bands are presented for DPSK and BFSK modulation/demodulation. The type of hit is categorised into five or eight hit types to represent a hit from a signal in adjacent hopping bands instead of the conventional two types of hits, i.e. partial and full hits.

The growing acceptance of the ATM as the transfer mechanism of the future B-ISDN, the increasing user requirements for portability and mobility and the increasing power of the portable devices, have led many researchers to investigate the transmission of ATM cells over a wireless medium. This paper discusses the necessary extensions to the B-ISDN protocol reference model, in order to support mobile applications. Finally, the IEEE 802.11 MAC layer protocol and its ability to transport ATM cells, preserving the delay requirements of the delay-sensitive applications, are investigated.

The packet reservation multiple access (PRMA) protocol was originally proposed for small cells. However, efficient channel utilisation of PRMA has encouraged research into its applicability to other communication technologies such as GSM/DCS and DECT (digital European cordless telecommunications). In this paper, we apply a modified version of PRMA, called burst reservation multiple access (BRMA), to full- and half-rate GSM/DCS as well as DECT. We then proceed to analyse the system performance using an equilibrium point Analysis (EPA). Finally, the performances of these adapted systems are evaluated. Results show that BRMA, with delayed feedback messages, considerably improves the capacity of these TDMA-based systems (up to 88%) while simultaneously satisfying a 1% speech packet dropping limit.

Various scenarios for GSM-satellite integration are discussed and optimised system architectures are proposed in terms of service requirement, implementation cost, routing of the signalling and modifications on the GSM network. The system architecture is defined by a particular network relationship and integration level. Three integration scenarios are proposed to support different service groups.

This paper presents a novel video coding algorithm which exploits past frame statistics for entropy coding of the gain-shape VQ parameters. A subband transform has been used to decorrelate the motion compensation residual in order to overcome the block visibility problem. The vectors with samples from different subbands are quantised using a gain-shape VQ technique which allows effective bit rate control. When compared to the H.261 standard, the proposed algorithm has given higher PSNR values at lower bit rates.

A TDMA-based multiplexing protocol is introduced as a candidate multiple access scheme, for an indoor radio LAN which is based on the ATM concept. This protocol attempts to provide high bandwidth utilisation and satisfy, the delay requirements of different types of services. The signaling for the radio link access is in accordance with that used at the user-to-network interface (UNI) of the public B-ISDN. The proposed solution deals with the problem of synchronizing various connections which belong to a multiconnection call and takes advantage of the discontinuous data generation which characterizes voice and file transfers.

Packet reservation multiple access (PRMA) and advanced time division multiple access (ATDMA) protocols (proposed in the RACE project such as PRMA++) are multiaccess protocols proposed for the third generation mobile communications systems. The main factor apart from channel impairments, which affects the performance of such protocols is collision either within an information time slot (in PRMA) or a reservation time slots (in PRMA++). These collisions waste available channel resources and can cause undesirable congestion and lower the service quality. We generalise the idea of PRMA which results in the upper-bound capacity calculation and reveals new insight into the relationship between the parameters of such protocols. The performance dependent parameters such as delay, throughput, statistics, capacity and packet dropping probability are mathematically analysed and generalised such that they can be applicable to all reservation-based multiple access schemes. Through such analysis the upper-bound performance for such protocols is derived. The sensitivity of the system performance to different system measures (such as throughput, delay, packet dropping statistics) are evaluated for a range of system parameters (bandwidth, number of users, voice activity factor). Finally, the performance of PRMA and PRMA++ with their upper-bound values are compared.

This paper presents a linear prediction (LP) based vocoder employing a novel technique which ensures smooth evolution of the synthetic speech waveform. In this coder, speech waveforms are considered as having a 'time envelope', the shape of which contains important perceptual information. By ensuring that the time envelope of the synthetic speech closely matches that of the original, natural sounding synthetic speech can be produced. Envelope matching may be achieved using a new, low complexity analysis by synthesis loop at the decoder which determines the synthetic excitation energy. The advantage over more traditional linear prediction vocoders is that the amplitude time envelope is preserved in addition to the spectral envelope, allowing the rapid amplitude transitions associated with onsets to be retained in the synthetic speech, resulting in a more intelligible output. Simply controlling the overall energy of the synthetic excitation is not sufficient to accurately control the synthetic speech energy. Small changes in linear prediction or pitch parameters due to quantization, for example, can cause variations in the synthetic speech amplitude, especially from one pitch cycle to the next resulting in noisy synthetic speech. The inclusion of an analysis by synthesis loop at the decoder ensures that the synthetic speech amplitude is independent of variations in the pitch period and LP parameters. This paper presents a complete vocoder scheme using time envelope matching, including details of techniques such as parameter interpolation, excitation pulse shaping and pitch tracking which have proven necessary to produce natural sounding synthetic speech at 2.4 kb/s and below.>

The authors present an 8 kb/s low delay speech coder which is based on the code excited linear prediction (CELP) algorithm. They concentrate on analyzing the problem areas in backward predictive systems and solutions to alleviate these problems. The authors report on a forward linear predictive coding adaptive scheme to eliminate such distortions. Another approach is to use a windowing technique in the frequency domain on the error signal in analysis-by-synthesis procedures. The adaptation of the long term predictor (LTP) coefficients is also considered in a backward and forward mode for differential pitch coding of the LTP lags. The role of the excitation gain update rate is also examined in providing higher quality and better adaptation of the gains for an efficient vector quantization procedure. An 8-kb/s coder with a buffering delay of 4 ms has been informally subjectively tested, and the latest test results indicate a performance equal to that of the GSM at worst case.>

Results from a multiband propagation experiment for a high elevation angle land-mobile satellite (LMS) channel are presented. A small helicopter was used to fly the transmitter module, transmitting frequencies in the L, S, and Ku bands. A vehicle equipped with the corresponding receivers and data acquisition system was followed by the helicopter on the selected routes. The measurement campaign was undertaken in two phases in September 1991 and in April 1992. The results show considerable decrease in signal attenuation when the path elevation angle is high due to reduced shadowing. In general, the attenuation increases with the increasing radio frequency. Foliage density has also been found to influence the fade levels, especially at higher path elevation angles. The overall analysis of the propagation data indicates that the fading character of the LMS channel is significantly dependent on the surrounding environment.>

Optimum quantization and code assignment schemes are described which minimize the subjective quality degradations introduced into the output speech of code excited linear predictive (CELP) coders by channel degradations. The background and basis for use of minimum redundancy for error control are examined. Greater emphasis is placed on adjustment of corrupted parameters to minimize subjective degradation rather than outright bit-by-bit error correction. These schemes are mostly tested on the CELP baseband coder, but they should be applicable to any linear predictive coder. They raise the bit rate of a 4.8-kb/s coder by about 12.5% and its MOS at 2*10/sup -2/ bit error rate by about 21.1% (scale 1-5).>

An improved CELP (code-excited linear prediction) baseband (BB) coder was tested using informal subjective listening tests. The overall bit rate of the coder was 4.7 kb/s. The subjective quality of speech scored just over three on a five-point mean opinion scale. Improvements are described that increase the score by about 0.35 over its original form. This means that in terms of quality the CELP BB coder at around 4.8 kb/s can replace the analog ACSSB operating even at 51 dB/Hz because in its original form it had subjective quality equivalent to ACSSB. To further investigate the performance of the coder the authors introduced random channel errors into the bit stream between the encoder and the decoder. At bit error rates of 10/sup -3/ and less, the coder did not need any forward error protection. When the bit error rate was around 10/sup -2/ an unexpected distortion occurred; the output energy level of the coder was very low whenever there were errors in the pitch filter or the optimum vector gain parameters. This was due to the new adaptation scheme used for the optimum vector gain. The authors solved this problem by adapting the optimum gain with the maximum block energy of the pitch filter memory or by simply using the energy of the whole of the pitch filter memory.>

A robust method is described for the determination of pitch in voiced speech. The spectral autocorrelation function measures the regular harmonic spacing in the spectrum of the speech signal by applying an autocorrelation to the power spectral density. It is shown that this method is capable of accurate pitch tracking in additive noise. The preprocessing is critical for good performance, and in this case the speech spectrum is flattened by obtaining the residual from linear prediction analysis and the original speech. Application of suitable postprocessing enables this method to operate over a wide range of human pitch down to very low signal-to-noise ratios.>

A baseband coder is discussed and its subjective quality compared with code-excited linear prediction (CELP) and vector-quantized transform coding at various bit rates from 9.6 to 4.8 kb/s. It is also with that CELP-BB coding is capable of producing natural, intelligible and smooth speech at 2.4 kb/s. The code-book search in CELP-BB requires no convolution. The pitch filter memory is subtracted from the original baseband signal to form the reference signal, which is directly matched by the code-book sequences. Because most of the computation is performed on the baseband, which is decimated, and during code-book search only the pitch filter response is considered, the complexity of CELP-BB is very much less than that of CELP and its speech quality is not affected by LPC quantization error to such an extent as in CELP.>

An adaptive predictive coder (APC) with backward adaptive short-term predictor is presented for operation at 16 kb/s. Adaptive postfiltering is applied in the output of the decoder. The performance of the coder is evaluated both objectively and subjectively for fixed and switched degrees of postfiltering. Based on a stimulus-response model for the subjective testing method the performance of the coder is expressed in terms of Q-equivalent values.>