Reliable group video call is one of the main services offered by future Mission-Critical Communications (MCC). To support its requirements, coordinated multi-point transmission in multi-cell environments is an attractive feature for MCC over Multimedia Broadcast Multicast Services owing to its potential for coverage improvement and multicast transmission. In such a scheme, full cooperation among all cells of an area achieves the highest cooperative gain, but has stringent impact on system capacity. A trade-off in the cluster's size of serving cells thus arises between high Signal to Interference plus Noise Ratio (SINR) and network capacity. In this paper, we formulate an optimization problem to maintain an acceptable system blocking probability, while maximizing the average SINR of the multicast group users. For every multicast group to be served, a dynamic cluster of cells is selected based on the minimization of a submodular function that takes into account the traffic in every cell through some weights and the average SINR achieved by the group users. Traffic weights are then optimized using a modified Nelder-Mead simplex method with the objective of tracking a blocking probability threshold. The proposed clustering scheme is compared to full cooperation and to Single-Cell Point-To-Multipoint (SC-PTM) schemes. Results show that dynamic clustering offers the best trade-off between coverage and capacity for MCC.

Mission-critical communications conveyed over Professional Mobile Radio (PMR) are characterized by a high level of reliability, an improved coverage and group call communications. Hybrid Automatic Repeat on re-Quest (HARQ) schemes are commonly used to provide a reliable communication over multipath noisy wireless channels. They, however, generate an excessive control signaling overhead on the uplink when downlink multicast is considered and groups include many members. In this paper, we propose a simple repetition scheme without request as an alternative to HARQ for group communications. When transport blocks are retransmitted several times, a tradeoff arises between coverage and capacity on the one hand, coverage and delay on the other hand. To evaluate the performance of our scheme, we use a link layer abstraction based on the Mean Instantaneous Capacity (MIC) together with BLER vs. SNR curves in AWGN. We carefully design our repetition scheme by considering the channel characteristics and the delay constraint imposed by video codecs. We show that up to 11 dB gain in SNR is achieved when compared to a scheme without repetition. System level simulations show that cell radius can be multiplied by three in a Multicast/Broadcast Single Frequency Network (MBSFN).

Cloud Radio Access Network (C-RAN) is a cost-effective solution for cellular operators which not only offers resource allocation and interference management flexibility, but also helps them enhance the energy efficiency of the network. The key character of the C-RAN architecture is a centralized Baseband Unit (BBU) pool which consists of high-capacity processing units and real-time virtualization. However, this centralized architecture can affect the system latency. As a consequence, the minimization of the execution delay of each user services in the BBU pool can be perceived as a major performance objective. In this paper, we consider different delay sensitive services and optimize their execution time inside the BBU pool. We present a new approach of BBU selection based on queuing theory in order to minimize the response time in the BBU pool under resource cost constraint. Simulation results showed that our proposed approach is more efficient than benchmark algorithms in terms of response time and throughput.

Multicast/Broadcast Single Frequency Network (MBSFN) is envisioned to be a key technology for business and mission critical communications. The need arises to define simple and efficient dimensioning rules for such networks. The Signal to Interference plus Noise Ratio (SINR) is an important key performance parameter since other metrics such as outage probability and capacity can be deduced from it. In this work, we propose an analytical model to derive an approximate closed-form formula of the SINR in a MBSFN. Our model takes into account Inter-Symbol Interference (ISI) due to the different propagation delays between the User Equipment (UE) and its serving evolved Nodes-B (eNBs). The comparison with Monte Carlo simulations shows that our approach provides accurate results when shadowing standard deviation is low. When shadowing is highly variable, our model, while less accurate, outperforms the traditional approach based on Fenton-Wilkinson. This phenomenon is due to the fact that several eNBs serve the same UE so that shadowing on every individual link compensate.

Long Term Evolution (LTE), designed by 3rd Generation Partnership Project (3GPP) to increase the capacity of radio mobile communications, has been endorsed by multiple public protection and disaster relief organizations as a next generation technology for Professional Mobile Radio (PMR) networks, which convey business and mission critical communications. One of the main services of PMR is the group communication that can be seen as a Multimedia Broadcast Multicast Service (MBMS). LTE offers functionality to transmit this type of flows either by MBMS over Single Frequency Network (MBSFN), or Single-Cell Point-To- Multipoint (SC-PTM). In this paper, we compare MBSFN, SC-PTM and unicast transmissions in terms of radio quality, system spectral efficiency and cell coverage. Our main conclusion is that SC-PTM together with Transmission Time Interval (TTI) bundling transmissions offers a flexible solution to trade coverage off for capacity.

Relay nodes-enhanced architectures are deemed a viable solution to enhance coverage and capacity of nowadays cellular networks. Besides a number of desirable features, these architectures reduce the average distance between users and network nodes, thus allowing for battery savings for users transmitting on the uplink. In this paper, we investigate the extent of these savings, by optimizing relay nodes deployment in terms of uplink energy consumption per transmitted bit, while taking into account a minimum uplink average user delay that has to be guaranteed. A novel performance evaluation framework for uplink relay networks is first proposed to study this energy-delay trade-off. A simulated annealing is then run to find an optimized relay placement solution under a delay constraint; exterior penalty functions are used in order to deal with a difficult energy landscape, in particular when the constraint is tight. Finally, results show that relay nodes deployment consistently improve users uplink energy efficiency, under a wide range of traffic conditions and that relays are particularly efficient in non-uniform traffic scenarios.

In this paper, we address the problem of optimally placing relay nodes in a cellular network with the aim of maximizing cell capacity. In order to accurately model interference, we use a dynamic framework, in which users arrive at random time instants and locations, download a file and leave the system. A fixed point equation is solved to account for the interactions between stations. We also propose an extension of a fluid model to relay based cellular networks. This allows us to obtain quick approximations of the Signal to Interference plus Noise Ratio (SINR) that are very close to 3GPP LTE-A guideline results in terms of SINR distribution. We then use these formulas to develop a dedicated Simulated Annealing (SA) algorithm, which adapts dynamically the temperature to energy variations and uses a combination of coarse and fine grids to accelerate the search for an optimized solution. Simulations results are provided for both in-band and out-of-band relays. They show how relays should be placed in a cell in order to increase the capacity in case of uniform and non-uniform traffic. The crucial impact of the backhaul link is analyzed for in-band relays. Insights are given on the influence of shadowing.

Location fingerprinting is a positioning method that exploits the already existing infrastructures such as cellular networks or WLANs. Regarding the recent demand for energy efficient networks and the emergence of issues like green networking, we propose a clustering technique to compress the radio database in the context of cellular fingerprinting systems. The aim of the proposed technique is to reduce the computation cost and transmission load in the mobile-based implementations. The presented method may be called Block-based Weighted Clustering (BWC) technique, which is applied in a concatenated location-radio signal space, and attributes different weight factors to the location and radio components. Computer simulations and real experiments have been conducted to evaluate the performance of our proposed technique in the context of a GSM network. The obtained results confirm the efficiency of the BWC technique, and show that it improves the performance of standard k-means and hierarchical clustering methods.

Location Fingerprinting is a localization technique which uses a radio database as the key element for the positioning process. Performance of location fingerprinting systems has been analyzed empirically in some previous works. However, there is a lack of theoretical models that analyze and predict the fingerprints behavior under different physical situations. In this work we present an analysis to evaluate the distinctiveness of fingerprints in a local neighborhood, in the context of cellular radio fingerprinting. The model is developed assuming the presence of correlated log-normal shadowing. Based on the presented analysis, we conclude some general guidelines for design and implementation of radio databases in fingerprinting systems.

In this paper we propose an analytical evaluation of the performance of the zero forcing precoding technique in terms of outage probability in a multicellular multiuser context. The channel model includes path loss shadowing and Rayleigh flat fading. Two cases are examined. The first one considers a constant lognormal shadowing. In this case, a closed form expression of the outage probability is derived. In the second case we consider a randomly variable lognormal shadowing and we propose an easily computable expression of the outage probability. Simulation results show the degradation of performance induced by the shadowing.

We present a propagation simulation model developed at TELECOM-ParisTech to assess performance of mobile radio networks. This model is consistent with the typical propagation model OSLN (one slope with log normal shadowing propagation model) considered by most authors. The new scheme, called Mondrian model, presents several interesting features: (i) it introduces correlations between powers measured on two nearby points, (ii) on a fixed location, path losses relative to stations with close azimuths are also correlated. This model can be used in different situations: evaluation of cellular network (e.g. handover simulation), fingerprint localization, dynamic RRM (radio resource management), cognitive radio and DSA (Dynamic Spectrum Allocation).

Extensive research in recent years has shown the benefits of cognitive radio technologies to improve the flexibility and efficiency of spectrum utilization. This new communication paradigm, however, requires a well-designed spectrum allocation mechanism. In this paper, we propose an auction framework for cognitive radio networks to allow unlicensed secondary users (SUs) to share the available spectrum of licensed primary users (PUs) fairly and efficiently, subject to the interference temperature constraint at each PU. To study the competition among SUs, we formulate a non-cooperative multiple-PU multiple-SU auction game and study the structure of the resulting equilibrium by solving a non-continuous two-dimensional optimization problem. A distributed algorithm is developed in which each SU updates its strategy based on local information to converge to the equilibrium. We then extend the proposed auction framework to the more challenging scenario with free spectrum bands. We develop an algorithm based on the no-regret learning to reach a correlated equilibrium of the auction game. The proposed algorithm, which can be implemented distributedly based on local observation, is especially suited in decentralized adaptive learning environments as cognitive radio networks. Finally, through numerical experiments, we demonstrate the effectiveness of the proposed auction framework in achieving high efficiency and fairness in spectrum allocation.

This paper proposes the utilization of GSM logical channels (RACH, AGCH and TCH) and UMTS signaling (MIB and SIBs) of the Broadcast Channel to transmit a Cognitive Beacon Channel (CBC). The CBC will help to improve spectrum awareness by conveying signalization to mobile users in a multi-Radio Access Technology (RAT) environment (e.g. 3GPP, Wi-Fi, WiMAX and future cognitive radio systems). Taking advantage of this spectrum knowledge, the purpose of the CBC is to transmit the necessary information to allow Dynamic Spectrum Access (DSA) using a centralized architecture. The principal motivation of this proposition is to obtain benefit from existing 3GPP technologies proved to be efficient and accepted. Simulation results show that our proposals, using logical channels of GSM and UMTS outperform, respectively, the On-demand and the Broadcast CPC implementations of the E2R II project.

Location Fingerprinting is one of the radio positioning techniques which has been proposed in the field of Location Based Services (LBS). Considering the actual trends towards energy efficient systems and green networking, reducing the energy consumption has become a challenging issue in the context of fingerprinting systems. In this paper we present a clustering technique which aims to compress the radio database and hence to reduce the online processing load of the system. We propose a hierarchical clustering method which is applied in a concatenated location-radio signal space. Computer simulations have been conducted to evaluate the performance of the proposed technique in environments with different shadowing configurations. The results show that the proposed clustering technique outperforms the conventional griding method, and besides allows us to reduce the size of the database significantly while keeping an acceptable level of performance for the positioning system.

In this paper, we present and analyze a Tabu Search (TS) algorithm for DSA (Dynamic Spectrum Access) in cellular networks. We study a mono-operator case where the operator is providing packet services to the end-users. The objective of the cellular operator is to maximize its reward while taking into account the trade-off between the spectrum cost and the revenues obtained from end-users. These revenue are modeled here as an increasing function of the achieved throughput. Results show that the algorithm allows the operator to increase its reward by taking advantage of the spatial heterogeneity of the traffic in the network, rather than assuming homogeneous traffic for radio resource allocation. Our TS-based DSA algorithm is efficient in terms of the required memory space and convergence speed. Results show that the algorithm is fast enough to suit a dynamic context.

In this paper, we present a game theoretical framework for DSA (Dynamic Spectrum Access) in cellular networks. We model and analyze the interaction between cellular operators with packet services, in a spectrum sharing context. We present inter-operator DSA algorithms based on game theory. A two-players non-zero sum game is formulated, where the operators are the players. We define a utility function, for the operator that takes: (1) the users throughput, (2) the spectrum price, and (3) the blocking probability into consideration. We present two system models: a) a centralized model where a DSA algorithm, for the global welfare in terms of the operators rewards, is inspired by the Pareto optimality concept. b) a distributed model, where a DSA algorithm is based on Nash equilibria concept. The convergence to NE in the distributed model is analyzed. The rewards of the operators in the centralized DSA algorithm are compared with those in the FSA (Fixed Spectrum Access) situation. The obtained rewards using the centralized DSA algorithm significantly exceed the FSA rewards. The obtained blocking probabilities are shown not to exceed the target value.

In this paper, we propose a way of achieving optimally in radio resource management (RRM) for heterogeneous networks. We consider a micro or femto cell with two co-localized radio access technologies (RAT), e.g. WLAN and HSDPA. RAT are mainly characterized by the data rates they offer at a given distance of the access point. Dual-technology mobile stations (MS) are initiating downlink sessions in the considered cell. A network controlled joint RRM algorithm is responsible to assign MS to a RAT, while taking into account the joint spatial distribution of already accepted MS, the current load of each RAT, the location of the newly accepted session and its influence on the global performance. In a study based on the Semi Markov Decision Process (SMDP) theory, we show how to obtain an optimal policy. Optimality is here defined through a utility function accounting for user satisfaction.

In this paper, we investigate the performance of adaptive beamforming while using subcarrier permutation PUSC in WiMAX cellular network. In the literature, it has been shown that frequency reuse 1 is possible for beamforming capable WiMAX networks but with partial resource utilization or base station coordination. In this paper, we show however that using distributed subcarrier permutation (PUSC) offers sufficient diversity to allow full resource utilization without the need of coordination. We study an IEEE 802.16e cellular network employing adaptive beamforming per PUSC Major Group. Performance is evaluated in terms of radio quality parameters and system throughput. Results are based on Monte Carlo simulations performed in downlink. The simulation results show that even with reuse 1 and full load conditions, outage probability can be reduced to an acceptable value.

In this paper, we evaluate the performance of a WiMAX network in different frequency reuse scenarios with and without adaptive beamforming technique. We study the possibility of deploying reuse 1 networks. Radio quality in terms of SINR and outage probability on one hand, and throughput on the other hand, are the parameters considered for this analysis. Extensive Monte Carlo simulations, based on effective SINR computation using abstraction model mean instantaneous capacity (MIC), have been performed in downlink. The simulation results show that some frequency reuse schemes with a very good global throughput performance result however into significant user outage. The improvement in performance due to adaptive beamforming is evaluated. The frequency reuse patterns satisfying the two parameters (outage and throughput) in the best possible way are being suggested (based on simulation results) for WiMAX networks.

We establish a closed form formula of the other-cell interference factor f for omni-directional and sectored cellular networks, as a function of the location of the mobile. That formula is based on a fluid model of cellular networks: The key idea is to consider the discrete base stations (BS) entities as a continuum of transmitters which are spatially distributed in the network. Simulations show that the obtained closed-form formula is a very good approximation, even for the traditional hexagonal network. From f, we are able to derive the global outage probability and the spatial outage probability, which depends on the location of a mobile station (MS) initiating a new call. Although initially focused on CDMA (UMTS, HSDPA) and OFDMA (WiMax) networks, we show this approach is applicable to any kind of wireless system such as TDMA (GSM) or even ad-hoc ones.

In this paper, we propose a new framework for the study of cellular networks called the fluid model and we derive from this model analytical formulas for interference, outage probability, and spatial outage probability. The key idea of the fluid model is to consider the discrete base stations (BS) entities as a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor, f, which is defined here as the ratio of outer cell received power to the inner cell received power. Although this factor has been firstly defined for CDMA networks (in particular UMTS and HSDPA), the analysis presented hereafter is still valid for other systems using frequency reuse 1, like OFDMA (WiMAX), TDMA (GSM with frequency hopping), or even ad hoc networks. A closed- form formula of f is provided in this paper. From f, we are able to derive the global outage probability and the spatial outage probability, which depends on the location of a mobile station (MS) initiating a new call. All results are compared to Monte Carlo simulations performed in a traditional hexagonal network.

In this paper, the problem of subchannel composition and allocation for the downlink of an OFDMA system is investigated. The subchannelization mode FUSC adopted in 802.16 is described and compared with dynamic subcarrier allocation algorithms. Performances are evaluated regarding spectral efficiency and complexity. Both single cell and multi-cell scenarios are considered.

In this paper, we propose a new framework for the study of cellular networks called the fluid model and we derive from this model analytical formulas for interference, outage probability, and spatial outage probability. The key idea of the fluid model is to consider the discrete base stations (BS) entities as a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on CDMA systems. This approach is however also applicable to other technologies like OFDMA. A closed-form formula of the downlink other-cell interference factor, f, is provided and compared to simulations performed in a traditional hexagonal network. From f, we are able to derive the global outage probability and the spatial outage probability, which depends on the location of a mobile station (MS) initiating a new call.

In this paper, we investigate packet scheduling and radio resource allocation in orthogonal frequency division multiple access (OFDMA) wireless networks. Each subchannel is a Rayleigh fading channel modeled by a finite state Markov channel (FSMC). The wireless fair service (WFS) packet scheduler is modified for a multi carrier and multi rate context. The proposed algorithm, named opportunist wireless fair service (OWFS), copes with both real time (RT) and non real time (NRT) traffic constraints. For both traffic classes, specific criteria of performance are compared with PLFS, a scheduler recently proposed for OFDMA.

Multistreaming and multihoming SCTP features give better performance than TCP for the transport of signaling in wired networks. More recently, some solutions have been defined for wireless environment (Xing et al., 2002), mobile SCTP (mSCTP) is a wireless extension that was proposed to take benefit from the multihoming feature for hand off. In this paper we use SCTP's multihoming feature and define a new type of control chunk in order to retrieve radio information from mobile and to use this information to improve the performance of SCTP in handoff situation. We propose modifications of the SCTP congestion control algorithms to take into account information sent by mobile to the network (GGSN) via QoS_Measurement_Chunk. This new mechanism is useful to perform inter RAT handover for data. The example studied here is between EGPRS and WLAN. The results obtained are compared with the standard SCTP and present an improvement of performance especially in terms of throughput

SCTP is a transport protocol that is used in wired networks to transport PSTN signaling. It provides interesting features (namely multihoming and multistreaming) to enhance the performances of information transport over cellular networks air interfaces (S. Kang and M. Fields, 2003). Some additional extensions have been defined to adapt SCTP in a wireless context (mSCTP) (W. Xing et al., 2002). However current approaches do not take into account radio information in cell reselection/handover process. This study proposes a new extension for the SCTP protocol which aims at improving the transport performance in wireless environments. We define for that purpose a new control chunk (named Qos_measurement_chunk). It allows the emission of radio information from the mobile to the SCTP peer in the network. These information can be used by the SCTP layer to adapt the transmission rate to the current radio transmission conditions (particularly useful in handover/reselection situation). The combined use of Qos_measurement_chunk and of the multihoming feature provide a data handover with a performance improvement. The obtained simulation results are compared with the standard SCTP and present better performance in terms of data throughput in the access network

This paper is part of an ongoing effort for the standardization of a new APCO Project 25 air interface for professional mobile radio. It describes the structure of the control channel for the 2-slot TDMA air interface. It presents the types of signaling messages involved, the structure of the multiframe and the priority scheduling algorithm for signaling messages on the common control channel CCH. The performance of the algorithm is analyzed in terms of signaling message delays

In this paper, the downlink of a multi-cell OFDMA system is considered. Rate adaptive optimization is investigated with minimum rate requirement and in presence of co-channel interference. A low-complexity subcarrier allocation scheme is proposed. A particular procedure provides limitation of co-channel interference by dynamically adapting the subcarrier reuse factor. A rate requirement violation (RRV) threshold is introduced to decide whether or not the interference limitation procedure is to be used. The performance is evaluated for variant user's rate requirement. The evaluation includes comparison of the cell global rate and the outage probability with existing heuristics

B3G networks will provide seamless data handover between different radio access technologies (RAT). In a near future, the WLAN access will be integrated in GPRS and UMTS radio access networks (RAN). During their communications, the subscribers will be able to switch automatically between the two technologies. In that case, their previous data transfer need to be re-established in the new RAT. This process must be carried out while minimizing the breakdown time and the data loss. This paper intends to evaluate the performances of handover policies between GPRS/UMTS and WLAN RAT and to propose adapted data handover strategies at layer two

In this paper, the rate adaptive optimization (RA) problem, which maximizes the sum of user data rates subject to total power constraint and individual guaranteed rates, is considered. Two tasks are commonly examined: bandwidth allocation and specific subcarrier assignment. A mechanism to provide a degree of fairness among users is coupled with the first task. Considering the second task, a novel algorithm, rate profit optimization algorithm (RPO), is defined to assign specific subcarriers to different devices of a multiuser downlink OFDM system. In RPO, a new approach is proposed to assign a conflicting subcarrier (best subcarrier for several users). This algorithm is shown to exhibit good results regarding spectral efficiency and fairness with a complexity significantly lower than the Hungarian algorithm.

Mobile ad hoc networks (MANETs) emerge as one of the most attractive technologies in radio networks. They are complex networks that are difficult to analyze due to their unpredicted and random high rate topological changes. Bandwidth limitations in such networks allows multicast to be an important routing solution, which reduces the communication cost via providing efficient saving in bandwidth and network resources. In this paper, we study the random graph as a model of such complex networks and we derive an analytical model for our proposed source routing-based multicast protocol (SRMP). This model, named reactive random graph (RRG), is investigated from the random graph theory, exploiting the phase transition behavior from the percolation theory. Based on our RRG model, we analyze critical properties in SRMP. Our main goal is to study and balance the tradeoff between multicast group connectivity and the optimum use of resources through minimizing the communication graph size. Useful results are drawn out through our work, providing us with significant factors for enhancing the performance of SRMP

This paper analyzes a TCP connection over UMTS radio access bearer in RLC acknowledged mode. The stacking of RLC and TCP protocols is highly beneficial for the global system behavior. Protocol mechanisms used by RLC are well adapted to wireless constraints and the ARQ function implemented by RLC hides the wireless channel unreliability to TCP. However, RLC protocol parameters have to be carefully tuned otherwise the TCP performance can degrade due to RLC. One of the factors that can influence the TCP performance is the RLC buffer size. We analyzed some of factors that affect the RLC buffer occupancy and we show that an insufficient buffer size degrades the TCP performance.

The issue of power control (PC) in the downlink of a cellular CDMA network is studied. Two approaches are discernible. The first uses the base-to-mobile-distance in order to allocate transmitted powers while the other is based on closed-loop control. The best achievable performance of a PC is evaluated for the downlink of a CDMA network. This paper then studies an almost optimal downlink power control. Numerical examples are presented in order to discuss the downlink PC performance.

Integration of cellular networks into the existing Internet world gives rise to some problems, mainly for the reason that protocol mechanisms defined and optimized for wired networks do not perform well when they are directly applied in wireless networks. In this paper we study an uplink TCP connection over the UMTS radio interface, when using a RLC entity in acknowledged mode. We suggest the introduction between TCP and RLC protocols of a specific mechanism called early error notification. Via this mechanism, a TCP sender is informed whenever a data segment is virtually discarded at the RLC level. Thus, a TCP sender detects in advance a segment loss at the RLC level without waiting for three duplicated acknowledgments or a timeout event.

In a wireless CDMA network a mobile is classically connected to the base station with the best received power level (R/spl times/L). The association (or the integration) of base station assignment with power control allows a given network to have better achievable performance. We investigate the association of base station assignment and power control in order to study the best achievable signal-to-interference ratio (SIR) behaviour. The existence of a feasible solution to the quality constraints problem, along with the choice of the base station assignment in order to have the minimal sum of transmitted powers, are discussed. This is done for a unique SIR target and for a multi-target environment. We also address two problems: the base station assignment as a function of network quality targets and best achievable performance which is represented by the highest achievable SIR for every possible BS assignment vector. This last value is computed with less computations than when it is directly calculated. Simulations show that appropriate base station assignment may give interesting capacity gains, especially for non-uniform distributions.

This paper investigates the effect of circuit switched transmissions over General Packet Radio Service (GPRS) performance. GPRS is an additional GSM service, which provides packet switched data services over GSM network and a packet access to data networks. Radio resources, available in a GSM cell, are shared dynamically between GPRS and GSM circuit switched services and the physical channels associated to GPRS are called Packet Data Channels (PDCH). In this paper, we propose new procedures of physical channels assignment to mobile stations in order to integrate voice transmissions (circuit switching) and data transmissions (packet switching) over GSM network. However, these procedures can be used for diversified types of TDMA-based wireless networks. The proposed protocols are described and their performance is evaluated. Besides, the performance of GPRS system is evaluated in the case of a fixed number of PDCHs. The effect of voice activities on GPRS performance is analyzed and evaluated considering the best effort performance parameters and World Wide Web (WWW) application.

We propose and present a new access persistence control mechanism for packet cellular networks, such as General Packet Radio Service (GPRS) system, in order to improve the MAC layer performance. The MAC layer in GPRS make use of slotted ALOHA protocol combined with a specific retransmission mechanism to establish the physical connection. The main object of the new mechanism is to avoid the mixture of retransmitted access request and the new ones. The primary profit is the decrease of the transmission attempts number needed to successfully transmit an access request. Thus, it decreases the delay of transmission of one access request and the access requests blocking percent.

The implementation of the emerging high bandwidth data services in the existing band limited mobile standards requires improvement in both spectral efficiency and coverage. This paper deals with an efficient deployment of mixed voice and high speed real-time data services served by GSM and Enhanced Circuit Switched Data (ECSD) respectively in hot-spot areas. This is achieved by the virtue of a distributed radio resource management architecture.

We investigate and evaluate the performance of two scheduling algorithms for forward link packet access: in CDMA based cellular networks. Both algorithms use round-robin scheduling, ensuring fair access to users in overlapping and non-overlapping areas. One method provides time diversity whereas the other provides time as well as space diversity to users located in the handoff regions. The performance is also compared with that of a conventional hard handoff.

For third generation mobile systems, the benefit of locally centralized architectures for resource allocation and management should be investigated in the micro-cellular environment. In this paper the concept of bunch defined as a group of base stations strongly interconnected is investigated. An interference-matrix based scheme (i.e. best packing strategy) for resource allocation is used and its performance in presence of location errors is evaluated through simulations.

Hybrid automatic-repeat-request/forward-error-correction (ARQ/FEC) schemes are commonly used to provide reliable transmission over noisy channels. At high channel error rate, hybrid type II ARQ/FEC strategies which do not discard packets in error, but combine them with suitable parity packets, have shown better performances. However it is usually assumed in the literature that the control is error free in both forward and backward directions. Without this assumption, a corrupted control makes the packet useless, which is then inevitably discarded. In this paper a hybrid type II ARQ/FEC scheme using a concatenated coding is proposed in a TDMA setting. This protocol is intended to operate under realistic conditions. To manage the reception of packets with corrupted control, an intelligent mechanism is introduced. Simulations have proven a gain in throughput when this mechanism is implemented.

An analytical and numerical evaluation by Gilhoussen et. al.(see IEEE Trans. Veh. Technol, vol.40, no.2, p.303-3121, 1991) of the capacity of a cellular radio CDMA system has been proposed. This evaluation has shown the interest of using spread spectrum techniques in the area of cellular radio systems. However, considering the computations made by Gilhoussen et. al. for the reverse link, we note the following: the calculations lead at a given moment to the evaluation of the average external interference for which a quantity is claimed only intuitively to be an upper bound. We construct a sequence of approximations for the average external interference, where the average external interference is the sequence limit. The claimed upper bound of Gilhoussen is also the first element of this sequence of approximations. We show by numerical means that the sequence is decreasing which justifies the claim of Gilhoussen.

We present an architecture for a system with multi-cell centralized packet access. In micro- or pico-cellular environments, the coverage overlap by adjacent antenna units arises naturally, which means that a signal emitted by a mobile terminal is multiple received. The whole service area of the system is parceled out into small coverage zones, to which channels are dynamically allocated. For such a dynamic channel allocation to be effective, the system has to attach the mobile terminals to the zones of allocation, based on the strength of the received signal. We study the problem of this fine-localization of the mobile terminals in the presence of fast fading.

Studies a mutual synchronisation technique between base stations (BSs) which operates over the air. First, the different possible structures for broadcast control channels (BCCHs) are presented with their main functionalities. A structure of a common BCCH for a group of BSs sharing the same carrier with time multiplexing is proposed. This common BCCH may be used to provide synchronisation. Existing mutual synchronisation algorithms are then reviewed. For such algorithms, each BS combines measurements (estimated time offset) from neighbouring BSs to determine its own time phase. Computer simulations based on a TDMA system are used to evaluate stability and convergence speed of the algorithm.>

This paper is concerned with cryptosystems offering perfect or unconditional secrecy. For those perfect-secrecy systems which involve using keys just once, the theory is well established; however, this is not the case for those systems which involve using a key several times. This paper takes a rigorous approach to the definition of such systems, and exhibits some new families of examples of systems providing perfect secrecy for which the number of keys is minimal.

A new vector coding (quantization) system and its application to speech waveforms are presented. This system consists of several permutation codes of Variant I. An algorithm for the system design is developed. An encoding procedure which minimizes the distortion and finds out the reproduction index to be transmitted using a algebraic method is proposed. The system was designed and tested for the encoding of speech waveforms. The results of experimental simulations show that this is a prospective vector coding scheme with simple encoding procedure, smaller memory required, and not large computational burden of the design algorithm.

An application of error-correcting codes to "write-once" memories (WOM's) as defined by Rivest and Shamir is studied. Large classes of "WOM codes" that are easily decodable are obtained. In particular, a construction allowing three successive writings of11bits on23positions is derived from the Golay code.

Any symbol in a redundant code can be recovered when it belongs to certain erasure patterns. Several alternative expressions of a given symbol, to be referred to as its replicas, can therefore be computed in terms of other ones. Decoding is interpreted as decoding upon a received symbol, given itself and a number of such replicas, expressed in terms of other received symbols. For linearq-ary (n,k)block codes, soft-decision demodulation and memoryless channels, the maximum-likelihood decision rule on a given symbol is formulated in terms ofr \leqn - klinearly independent replicas from the parity-check equations. All replicas deriving from therselected replicas by linear combination are actually taken into account in this decision rule. Its implementation can be direct; use transformations or a sequential circuit implementing a trellis representation of the parity-check matrix. Ifr = n - k, decoding is optimum, in the sense of symbol-by-symbol maximum-likelihoed. Simplification results in the transformed and sequential implementations whenr < n - k. If the selected replicas are disjoint, generalized (q-ary, weighted) threshold decoding results. The decoding process can easily be modffied in order to provide word-by-word maximum-likelihood decoding. Convolutional codes are briefly considered. Two specific problems are discussed: the use of previous decisions, which leads to a weighted generalization of feedback decoding, and the extension of replication decoding to nonsystematic codes.

Transposing a computation of Mac Williams we derive an exact expression for, and a straightforward upper bound on, the residual error rate of a binary block code with a "standard" decoder. We also give series expansions for decoding error probability and residual error rates.