Carlo Nobile

The RRA-ISA multiple access protocol with and without simple priority schemes for real-time and data traffic in wireless cellular systems

A multiple access protocol, based on a Reservation Random Access (RRA) scheme, is derived for a wireless cellular network carrying real-time and data traffic. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over an entire frame. This is achieved by deciding on the access rights at the cell base station, which then broadcasts this information at the beginning of the frame. The decision is made on the basis of binary channel feedback information (collision/no collision) over the previous frames, as well as of long term averages of packet generation rates at the mobile stations, assuming independence in the presence of packets at the latter. The resulting protocol has therefore been termed Independent Stations Algorithm (ISA), and the overall scheme RRA-ISA. As in other RRA protocols, time constrained (e.g., voice) traffic operates in a dynamic reservation mode, by contending for a slot in the frame with the first packet of a burst, and then keeping the eventually accessed slot for the duration of the burst; packets of the time constrained traffic unable to access a slot within a maximum delay are dropped from the input buffer. No such constraint is imposed on data traffic. Together with the “basic” version of the access algorithm, three other variants are presented, which exploit three simple different priority schemes in the RRA-ISA “basic” structure, in order to give a prominence to the voice service. The aim of these variants is to improve the performance in terms of the maximum number of stations acceptable in the system, by slightly increasing the data packets delay. All the proposed schemes are analyzed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols that use ALOHA as a reservation mechanism (RRA-ALOHA or PRMA schemes).

Analysis and performance comparison of the RRA-ISA multiple access protocol for packet voice and data cellular systems

A multiple access protocol based on a reservation random access (RRA) scheme is derived, and its performance is evaluated and compared by simulation to that of other protocols operating within the same environment. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over an entire frame. This is achieved by deciding on the access rights at the base station, which then broadcasts this information at the beginning of the frame. The decision is made on the basis of binary channel feedback information (collision/no collision) over the previous frames, as well as of long term averages of packet generation rates at the mobile stations, assuming independence in the presence of packets at the latter. The scheme is analysed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols that use ALOHA as a reservation mechanism (RRA-ALOHA or PRMA schemes).

Prediction of Short-Term Evolution of Cloud Formations Based on Meteosat Image Sequences

In this paper an algorithm to predict the short-term evolution of cloud formations with high rainfall probability by using image sequences coming from meteorological satellites (Meteosat images) is described. The proposed algorithm consists of four steps: the first step performs image processing procedures (thresholding and relaxation, edge following, frequency filtering) adapted to a specific environmental application; the second step is dedicated to solve the correspondence problem in different images while the third one deals with the problem of modelling the parameters defining the time evolution of a cloud formation and investigates how these parameters can be estimated. The last step concerns the motion prediction of processed clouds. The main goals of this work are to test the effectiveness of the proposed procedure with different values of the filtering parameters, and to verify the importance and the influence of the mentioned parameters in the prediction mechanism. Some experimental results obtained by using real image sequences coming from Meteosat satellites are shown.

Performance of simple priority schemes for the RRA-ISA multiple access protocol in packet voice and data cellular systems

A multiple access protocol based on a reservation random access (RRA) scheme is derived, together with three of its variants, and their performance is evaluated and compared by simulation with that of another protocol operating within the same environment. Given a TDMA framed channel and a cellular structure, the aim of the protocol is that of maximizing the one-step throughput over on entire frame. This is achieved by deciding on the access rights at the base station, which then broadcasts this information at the beginning of the frame. The resulting protocol is termed the independent stations algorithm (ISA), and the overall scheme the RRA-ISA. As in other RRA protocols, time constrained (e.g., voice) traffic operates in a dynamic reservation mode, by contending for a slot in the frame with the first packet of a burst, and then keeping the eventually accessed slot for the duration of the burst; packets of the time constrained traffic unable to access a slot within a maximum delay are dropped from the input buffer. No such constraint is imposed on data traffic. The three different variants which are presented. This improvement is achieved by applying three different priority schemes which give a prominence to the service of the voice traffic. The different schemes are analysed by simulation in the presence of voice and data traffic. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) of ISA schemes over other protocols that use ALOHA as a reservation mechanism.

A call admission control strategy for multiservice wireless cellular packet networks

A simple connection control system for multiservice cellular wireless networks is presented. Mobile stations are classified depending on the traffic they generate (e.g., voice, data). Within each class, two subclasses are also identified: stations which have originated inside the cell and stations which come from adjacent cells. The connection control mechanism is carried out by considering a number of priorities among the various classes and their subclasses. It works on two levels: static and dynamic. The static level looks at “packet-level” quality of service (QoS), such as cell loss and delay, while the dynamic level takes care of connection dynamics and allows the load of the system to be driven with respect to the various subclasses. Results that illustrate the performance of this control mechanism are presented.

Dynamic bandwidth sharing between voice and data traffic in a RRA multiple access scheme for cellular mobile radio networks

Within the class of reservation random access (RRA) protocols, RRA-ISA operates over a TDMA framed channel in a cellular structure, with the aim of maximizing the one-step throughput over an entire frame. In the presence of mixed (e.g. voice and data) traffic, an additional dynamic bandwidth allocation technique has been introduced, in order to give a better service to the real-time traffic, subject to a quality constraint, by slightly increasing the data packet delay. Several comparisons show a relevant performance improvement (in terms of data delay and maximum number of voice stations acceptable within a cell) over other protocols.

A call-level access control strategy for integrated services wireless packet networks

A simple call admission control system for multiservice wireless networks is presented. By means of it, connection requests coming from different “classes” of traffic (i.e., voice, data) are regulated in order to meet a set of Quality of Service (QoS) constraints. The admission mechanisn works on two levels: a static and a dynamic one. The static level looks at “packet-level” QoS, such as cell loss and delay, while the dynamic level takes care of call dynamics and allows to drive the load of the system with respect to the various traffic classes. Whenever a connection recpiest for the n-th traffic class appears, both levels of control intervene and the call is accepted if both of them do not reject it. The decision at the static level is deterministic, and it is based on the concept of Schedulable Region; the decision at the dynamic level is probabilistic and it is based on the concept of Input Rate Region, which is explained in the paper. Results that show the performance of this control mechanism are presented.

A multiple access protocol with explicit and implicit reservation

A new version of a MAC-level protocol is introduced and investigated, operating in a cellular environment, where a base station co-ordinates mobile users within each cell. The channel multiplexing structure is based on time division, and the slots in each frame are dynamically assigned to the users and their service classes by the cell base station. Decisions are taken on the basis of binary channel feedback information (collision/no collision), by assuming independence in the presence of packets at the mobile stations, and aim at maximizing the one-step throughput in the current frame. The frame is divided into two periods: the first (short) one contains a number of minislots, equal to the number of ‘real’ slots (i.e. those capable of containing a fixed size packet) of the second part. At the beginning of the frame, the access rights are computed and broadcast to the users; the enabled stations that have a packet to transmit respond, by sending a short burst that contains their ID in a minislot. This most recent feedback is used at the base station to update the parameters of the decision algorithm, which is then re-applied to yield the final access rights for the second part of the frame. The performance of the scheme is analysed by simulation in the presence of mixed voice and data traffic, and compared with those of a reservation random access protocol using the same algorithm in a single-phase fashion (RRA-ISA) and PRMA. Copyright

A Combined Forward Error Control and Multiple Access Protocol for Wireless Voice/Data Integration

Different strategies for error control are investigated, in conjunction with a MAC-level protocol, operating in a multimedia noisy cellular environment, where a base station co-ordinates mobile users within each cell. The channel multiplexing structure is based on Time Division (TDM), and the slots in each frame are dynamically assigned to the users and their service classes. The access rights are decided by an algorithm, namely, the Independent Stations Algorithm (ISA), at the cell base station, which broadcasts this information to the users. Each single mobile station is associated a bit error probability, which changes with time in a random fashion. Bit error probabilities are estimated and the protection level of the Forward Error Correction (FEC) code is dynamically adapted to the new conditions. The performance of the scheme is analyzed by simulation in the presence of mixed voice and data traffic, and with different error handling techniques (FEC and Automatic Retransmission Request (ARQ)).

An integrated multiple access and hierarchical coding scheme for video communication on wireless networks

A Medium Access Control (MAC) protocol of the Reservation Random Access (RRA) family is integrated with a hierarchical video-coding scheme, to realize effective real-time video services over the up-link of a mobile wireless network. For every picture or for each group of contiguous pictures (GOP), the encoder generates an information set organized in a hierarchical layered structure. The base layer contains the information needed to a low quality video; the other layers contain data, which, if received and decoded, can enhance the video quality. The basic idea is to reserve bandwidth only to grant the transmission of base layer information, and modify the MAC scheme to manage the video enhancement data together with voice/dota streams. by adaptively transmitting the increimental video information only it the performances of other traffic classes will not drop below a certain threshold. The aim or this proposal is the improvement of the video stream quality in low load conditions, without a significant reduction of other traffic classes performance during high load periods. Several simulation results show the effectiveness of the proposed method.