Device-to-Device (D2D) communications are currently attracting high interest from industry and academia, targeting at new commercial and public safety proximity services (ProSe). A major challenge under consideration is the device discovery problem, i.e., the problem of meeting the communication peers in time, frequency and space. In line with the current standardization efforts from the 3rd Generation Partnership Project (3GPP), we propose a centrally controlled device discovery scheme which consists of an application layer procedure and a set of access level enhancements. The target of the application layer procedure is to enable the ProSe discovery services, while the access level enhancements ensure the spectrum resources required for discovery transmissions. Evaluation results illustrate the impact of consuming cellular resources for device discovery on cellular network performance, while reveal the potential performance gains for the cellular network due to the introduction of the ProSe communications.

In this paper, we describe and evaluate an advanced traffic scheduler for IEEE 802.16 point-to-multipoint networks, referred to as "Colored Frame Registry Tree Scheduler" (C- FRTS). The main characteristics of this scheduler are i) the use of a tree structure to prepare the creation of time frame maps and reduce processing requirements at the beginning of each frame, and ii) a colored discrimination of packets scheduled for transmission to guarantee the bandwidth reserved for different connections. Simulation results show that C-FRTS can guarantee major QoS parameters, such as the maximum latency and the minimum and maximum reserved bandwidth, as well as provide differentiated treatment to the various service types.

The IEEE 802.16 standard provides a high degree of flexibility for setting up and operating wireless broadband networks in metropolitan environments. The standard supports numerous capabilities, including mesh topologies and multimedia communications. In this paper, we study these two features by investigating how efficiently an IEEE 802.16 mesh network can treat distributed multimedia traffic by providing differentiated quality of service (QoS). A key component of the system is the ldquoenhanced frame registry tree schedulerrdquo (E-FRTS) that provides QoS-aware resource allocation using a tree structure to prepare the creation of time frames and reduce processing requirements at the beginning of each frame. Simulation results show that distributed multimedia traffic can be efficiently supported in mesh 802.16 networks, provided efficient scheduling and a reasonable number of hops.

Abstract In this paper, we address the architecture and the procedures that can enable voice call handover from UMTS to WLAN and we also study how efficiently the WLAN can support the voice calls transferred from UMTS. Our study is based on a practical simulation model that lets us quantify the maximum number of voice calls that can be handed over from UMTS to WLAN, subject to maintaining the same level of UMTS QoS and respecting some WLAN policies. In addition, several other voice call performance metrics are derived. Our results indicate that an IEEE 802.11e access point can support a limited number of voice calls handed over from UMTS, which depends primarily on the applied WLAN bandwidth sharing policy (i.e., how the bandwidth is shared between WLAN voice and data users) and the QoS requirements. The performance of the WLAN scheduling algorithm is also of paramount importance and in our study we consider the so‐called ARROW scheduler. Although the simulation results are derived for a specific bandwidth sharing policy, they can readily be scaled and provide practical upper bounds for the number of UMTS voice calls that can be seamlessly admitted to a WLAN access point. Copyright © 2007 John Wiley & Sons, Ltd.

This paper studies the packet data transmission performance in Terrestrial Trunked Radio (TETRA) networks, giving particular emphasis on the performance of applications characterized by occasionally transmitting small messages between radio terminals and a fixed server. Such applications are constantly increasing in public safety networks and so does the need to dimension and configure TETRA networks in order to meet their reliability, delay and loss requirements. That was the main motivation of our performance analysis. We present simulation results for a variety of practical scenarios and we quantify key performance indicators such as the delay and loss rate characteristics. Our results can help in dimensioning and planning TETRA networks, and in particular in determining the number of packet data terminals that can be supported in a cell for a given traffic profile and QoS requirements.

In this paper we study the impact of voice traffic on the performance of packet data transmission in Terrestrial Trunked Radio (TETRA) networks. Emphasis is given on the performance of applications characterized by occasionally transmitting small messages between a number of radio terminals and a fixed server, while these terminals are also conducting group voice calls. We present simulation results for practical scenarios and discuss how key performance indicators such as the delay and loss rate characteristics are affected by the group call activity of the radio terminals. Our results can help in dimensioning and planning TETRA networks, and in particular, in determining the number of packet data terminals that can be supported in a cell for a given traffic profile and QoS constraints.

In this paper we propose and study a cross-layer mechanism that can improve real-time QoS provisioning over IEEE 802.16 metropolitan area networks. This mechanism utilizes information provided by the Physical and MAC layers and using a heuristic algorithm it derives new operational parameters for the Physical and Application layers, which can improve the performance of real-time applications. The main idea is to coordinate the adaptive modulation capability of the Physical layer and the multi-rate data-encoding capability of modern real-time applications in order to avoid inefficiencies caused by their independent operation. Simulations show that the proposed mechanism can assist 802.16 systems better adapt to frequent channel and traffic changes, leading to considerably reduced packet loss rates, especially under heavy traffic conditions.

In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as ARROW (adaptive resource reservation over WLANs), which aims at providing improved performance for the support of multimedia traffic. The novel characteristic of this algorithm, compared to previous proposals, is that it performs channel allocations based on the actual traffic buffered in the various mobile stations, i.e., on the exact transmission requirements. This feature renders ARROW ideal for variable bit rate traffic. However, an enhancement is also presented that improves ARROW performance under constant bit rate traffic. The ARROW algorithm and its enhancement are discussed and evaluated against two other schedulers found in the open technical literature, namely the simple scheduler and SETT-EDD. Results from a detailed simulation model verify that ARROW provides much better channel utilization and considerably improved performance, in terms of mean delay and packet loss

In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as ARROW (adaptive resource reservation over WLANs), able to handle multimedia traffic. The novel characteristic of ARROW is that it performs channel allocations based on the actual traffic (not estimated traffic) buffered in the various mobile stations. Additionally, a variation of ARROW is studied for improving the performance for constant bit rate traffic. The ARROW algorithm and its enhancement are evaluated against two other schedulers found in the literature, namely the simple scheduler and SETT-EDD. Results from a detailed simulation model show that much better channel utilization and considerably improved performance can be provided.

Currently, there is a strong need for integrating WLANs with 3G data networks and develop hybrid mobile data networks, capable of ubiquitous data services and very high data rates in hotspots. This paper addresses this need by proposing and discussing some architecture capable to provide interworking between WLANs and 3G networks and meet the requirements of two typical scenarios, which feature the highest market interest. These architectures can enable 3G subscribers to benefit from high throughput IP connectivity in strategic locations and also to maintain service consistency across several radio access technologies, such as IEEE 802.11, HiperLAN/2, UTRAN, GERAN, cdma2000, etc.

The media access control (MAC)-layer performance of the cellular digital packet data (CDPD) forward channel is studied and a new technique to improve the performance is proposed. The study is based on a computer simulation model wherein a CDPD base station continuously transmits a sequence of packets to a CDPD mobile station. We consider a Rayleigh fading channel and demonstrate how the performance metrics are affected by the channel characteristics. At the reception stage, we consider both coherent and differential reception. We argue that the throughput at the MAC layer is affected not only by the error performance of the physical layer, but also by several design characteristics of the MAC layer, including the block length and the alignment between blocks and packets. We illustrate the block error rate, packet error rate, and throughput performance by simulation results, and we show how the receiver may discard data, which is correctly received but nevertheless useless. Our main conclusion is that the CDPD forward-channel performance could be significantly improved should the identified deficiencies are eliminated. For this purpose, we propose a new automatic repeat request (ARQ) protocol that operates in the MAC layer to correct the erroneous blocks by means of retransmissions, and we study its performance. In addition, we discuss an adaptive scheme that maximizes the forward-channel performance by automatically enabling and disabling the ARQ protocol according to the channel conditions.

The paper focuses on the integration of Internet and wireless LANs (WLANs) and proposes a novel technique that supports seamless and efficient integration. This technique is based on a generic adaptation layer, referred to as wireless adaptation layer (WAL), which is introduced between the IP layer and the WLAN link layer. WAL is designed to: (i) cope dynamically with wireless channel impairments; (ii) provide QoS interworking between the IP infrastructure and the WLAN; (iii) be independent of the WLAN technology. These characteristics account for the advantages of WAL, namely, improved performance, wide applicability and provisioning of differentiated services.

A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a review of the current power-saving protocols is given. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable units) and a central administration authority that synchronizes the receivers. Some drawbacks of the synchronous operation lead us to the introduction of an asynchronous power-saving protocol, where no central synchronization is necessary and where each terminal may control its power consumption relative to its current needs. According to the proposed power-saving page-and-answer protocol, an acknowledgment paging procedure is preceding every packet transmission in order to alert mobile terminals with pending traffic. Steady-state performance is evaluated with the aid of simulation. The relationship between the achieved power-saving and the mean packet delay degradation is presented. Finally, we express some notable implementation issues and some considerations regarding the employment of this protocol as a supplementary power-saving service in microcellular mobile data networks and wireless local area networks.