http://hdl.handle.net/2117/7266 2013-06-19T01:47:14Z http://hdl.handle.net/2117/18796 Title: Analysis of the hidden and exposed terminal effects in wireless networks with cooperative ARQ Authors: Alonso-Zarate, J.; Alonso Zárate, Luis Gonzaga; Kormentzas, Georgios; Verikoukis, Christos Abstract: Cooperative Automatic Retransmission Request (C-ARQ) schemes allow those users which overhear a transmission to act as spontaneous relays when a packet has been received with errors at destination. When these users assist a source-destination pair in the retransmission process, the area exposed to the original transmission increases in comparison with non-cooperative ARQ schemes. In addition, the extension of the transmission time, due to the retransmissions, increases the vulnerability of a transmission to the hidden terminal problem. The paper provides a performance analysis of the hidden and exposed terminal effects in an 802.11-based wireless network where a C-ARQ scheme is executed at the Medium Access Control (MAC) layer. The presented analysis is supported by computer-based simulations. 2013-04-15T14:15:59Z http://hdl.handle.net/2117/18578 Title: Analysis of energy efficient distributed neighbour discovery mechanisms for machine-to-machine networks Authors: Vazquez, Francisco; Alonso-Zarate, J.; Alonso Zárate, Luis Gonzaga; Dohler, Mischa Abstract: Energy efficiency is one of the main challenges of Machine-to-Machine (M2M) networks, since they aim at connecting devices with limited access to power sources and operate without human intervention. It has been shown in the past that the use of short-range cooperation between wireless devices equipped with multiple Radio Access Technologies (RATs) can achieve energy savings and extend the lifetime of cellular wireless networks. Devices with cellular connectivity can become temporary gateways to provide energy-constrained devices within the short-range cluster with access to the long range cellular infrastructure. To this end, the devices need to discover their neighbours using their short-range radio interface to identify and select potential gateway candidates. Existing neighbour discovery mechanisms perform poorly in terms of delay and energy consumption to maintain, continuously at each device, complete neighbourhood information, and thus may not be suitable for energy-constrained M2M networks. In this paper, we focus on distributed neighbour discovery mechanisms that are initiated dynamically and spontaneously by a single device to discover only its single-hop neighbours. We formulate accurate delay and energy models of three discovery mechanisms based on frame slotted-ALOHA and contention tree algorithms, and compare their performance in terms of delay and energy consumption. 2013-04-03T14:15:55Z http://hdl.handle.net/2117/17413 Title: Experimental study of bluetooth, ZigBee and IEEE 802.15.4 technologies on board high-speed trains Authors: Higuera Portilla, Jorge Eduardo; Kartsakli, Elli; Valenzuela González, José Luis; Alonso Zárate, Luis Gonzaga; Laya Romero, Andrés Ernesto; Martínez, Raquel; Aguilar, Alicia Abstract: This paper studies the feasibility of using low-power wireless technologies such as Bluetooth, IEEE 802.15.4 and ZigBee in high-speed railway scenarios that involve bidirectional ground-to-train communication. The presented results have been obtained through experimental tests conducted at the Madrid- Barcelona high-speed rail line. A multiplatform communication system has been installed in a high-speed train, circulating at velocities up to 300 km/h, whereas autonomous devices have been disseminated along of the railway path to communicate with the onboard devices. The conclusions drawn from this work will be used as guidelines for the future implementation of autonomous communication platforms for high-speed rail connectivity. 2013-01-17T19:28:24Z http://hdl.handle.net/2117/17154 Title: Comparison of multicast/broadcast services in long term evolution advanced and IEEE 802.16m networks Authors: Calabuig Gaspar, Jorge; Monserrat del Río, José Francisco; Martín-Sacristán Gandía, David; Olmos Bonafé, Juan José Abstract: This paper performs a comparison of multicast/broadcast services (MBS) support in Long Term Evolution Advanced (LTE-A) and Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16m. Firstly, the main technical features of both standards concerning MBS operation are presented. It is shown that WiMAX offers higher unicast/MBS multiplexing flexibility as it supports both frequency and time multiplexing schemes, whereas LTE-A only includes time multiplexing. Besides, onlyWiMAX supports multi-antenna transmission. Next, the results of two simulation-based assessments are presented. In the former, it is considered a scenario with all cells transmitting the same MBS service. The effect of inter-site distance (ISD) on themaximum MBS data rate is evaluated. Results show thatWiMAXconfigurations outperform LTE-A for small ISD. This is becauseWiMAX provides a higher number of resources dedicated to data transmission for the same bandwidth. Furthermore, some WiMAX configurations support two spatially multiplexed data streams. With higher ISDs, LTE-A outperforms single-stream WiMAX configurations. In the second assessment, a MBSFN area surrounded by interfering cells is considered to compare unicast/MBS multiplexing performance. The higher maximum MBS data rate is achieved inWiMAX with time division multiplexing, which is precisely the only alternative included in LTE-A 2012-12-19T14:19:45Z http://hdl.handle.net/2117/16500 Title: On the need for dynamic downlink intercell interference coordination for realistic long term evolution deployments Authors: González González, David; García Lozano, Mario; Ruiz Boqué, Sílvia; Olmos Bonafé, Juan José Abstract: Intercell interference is the main issue limiting the capacity of modern orthogonal frequency-division multiple access based cellular networks. Recently, extensive research work has been carried out in this field, and intercell interference coordination techniques have been recognized as key enablers of current (and future) cellular technologies. In this article, (i) a comprehensive survey of the most representative contributions is provided together with (ii) a generic methodology to measure their actual merit. The performance of several interference avoidance strategies has been evaluated both from system and user point of view in the context of a Long Term Evolution (LTE)-based network considering not only synthetic cellular scenarios but also realistic deployments. Our literature review indicates that there is a need for adaptive/operatorcustomizable low-complex intercell interference coordination (ICIC) schemes suitable for realistic LTE deployments. Results obtained by means of a comprehensive set of simulations corroborate and support this premise. In this article, it is shown that simultaneous gains in terms of spectral/energy efficiency and fairness can be achieved through dynamic mechanisms with respect to both classic hard reuse schemes and static ICIC techniques. Besides numerical results, a novel merit assessment methodology based on several weighted performance metrics is proposed. Our findings show that dynamic schemes outperform static techniques by around 20–35% in realistic deployments. 2012-09-14T11:47:49Z http://hdl.handle.net/2117/16496 Title: Throughput analysis of a cooperative ARQ scheme in the presence of hidden and exposed terminals Authors: Alonso-Zarate, J.; Alonso Zárate, Luis Gonzaga; Kormentzas, Georgios; Tafazolli, Rahim; Verikoukis, C. Abstract: Cooperative Automatic Retransmission Request (C-ARQ) schemes exploit the broadcast nature of the radio channel by allowing those users which overhear a transmission to act as spontaneous relays when a packet has been received with errors at destination. Transmission takes place in two phases. First, the source transmits to the destination. In the case of error, retransmissions are then executed by the relays, providing the system with cooperative diversity. In this paper we analyze how the addition of these relays to the communication modifies the well-known hidden and exposed terminal problems associated to any medium access control protocol based on carrier sensing. This work is focused on Carrier Sensing Multiple Access (CSMA) protocols, such as the one defined in the IEEE 802.11 Standard. The theoretical study presented in this paper has been supported by computer-based simulations. 2012-09-14T11:12:36Z http://hdl.handle.net/2117/15779 Title: Saturation throughput performance analysis of a medium transparent MAC protocol for 60 GHz radio-over-fiber networks Authors: Kalfas, George; Pleros, Nikos; Tsagkaris, Kostas; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos Abstract: We demonstrate an analytical model for calculating the saturation throughput performance of a medium transparent medium access control (MAC) protocol in 60 GHz radio-over-fiber (RoF) networks. The proposed model incorporates effectively the medium transparent MAC mechanism, assuming a finite number of terminals and ideal channel conditions. It takes into account contention both at the optical and wireless layer, ensuring seamless and dynamic capacity allocation over both transmission media. This model enables extensive saturation throughput performance analysis for the medium transparent MAC and has been applied to 60 GHz RoF network scenarios considering variable numbers of available optical wavelengths, wireless nodes and serving antenna elements and for two different data rate values, namely 155 Mbps and 1 Gbps. Comparison between the model-based throughput results and respective simulation-based outcomes reveals that our model is extremely accurate in predicting the system throughput. Moreover, it confirms that the proposed medium transparentMAC protocol can effectively operate in high-speed 60 GHz RoF LAN environments. 2012-05-06T17:00:40Z http://hdl.handle.net/2117/15136 Title: HetNets: la gestió de la interferència Authors: García Lozano, Mario; Giupponi, Lorenza 2012-02-14T18:44:51Z http://hdl.handle.net/2117/12770 Title: Static Inter-cell interference coordination techniques for LTE networks: a fair performance assessment Authors: González González, David; García Lozano, Mario; Ruiz Boqué, Sílvia; Olmos Bonafé, Juan José Abstract: This paper focuses in the analysis of 100% static and distributed inter-cell interference coordination techniques in the context of LTE networks. Several methods have been modeled and studied with the aim of deriving practical radio planning rules based on the joint effect of operational parameters and thresholds. The investigation places special emphasis on the efficiency vs. fairness tradeoff through a set of metrics that allow not only to evaluate the measurements from different points of view, but also to look at the effectiveness in radio resources usage. Results show that similar levels of spectral efficiency can be achieved by means of a proper and accurate network tuning. Moreover, interesting second order differences appear due to inherent features of each approach. These can be exploited depending on the particular network operator needs. 2011-06-14T16:57:26Z http://hdl.handle.net/2117/12754 Title: Multi-radio cooperative ARQ in wireless cellular networks: a MAC layer perspective Authors: Alonso Zárate, Jesús; Kartsakli, Elli; Katz, Marcos; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos Abstract: Multi-Radio Cooperative Automatic Retransmission Request (MCARQ) schemes are introduced in this paper within the context of hybrid networks which combine long-range and short-range communications. Since the number of wireless devices is incessantly increasing, it is frequently possible to establish a spontaneous cooperative cluster in the close proximity of any wireless device. These devices forming the cluster are connected to both a cellular-based network such as WiMAX, 3G, or LTE and a short-range network based on technologies such as WLAN, Zigbee, Bluetooh, or UWB, among other possibilities. The main idea behind the proposed MC-ARQ scheme is that, upon transmission error through the cellular interface, retransmission can be requested to the wireless grid surrounding the destination device using the short-range interface instead of the primary cellular link. Therefore, besides the cooperative diversity attained with CARQ schemes, the traffic load in the cellular interface is reduced benefiting thus a high number of users and reducing both energy consumption and interference. The Persistent Relay Carrier Sensing Medium Access (PRCSMA) protocol is presented as an example of solution for the MAC layer in this emerging new topic. 2011-06-09T14:34:11Z http://hdl.handle.net/2117/12309 Title: Secure precise clock synchronization for interconnected body area networks Authors: Sánchez Sánchez, David; Alonso Zárate, Luis Gonzaga; Angelidis, Pantelis; Verikoukis, Christos Abstract: Secure time synchronization is a paramount service for wireless sensor networks (WSNs) constituted by multiple interconnected body area networks (BANs). We propose a novel approach to securely and efficiently synchronize nodes at BAN level and/or WSN level. Each BAN develops its own notion of time. To this effect, the nodes of a BAN synchronize with their BAN controller node. Moreover, controller nodes of different BANs cooperate to agree on a WSN global and/or to transfer UTC time. To reduce the number of exchanged synchronization messages, we use an environmental-aware time prediction algorithm. The performance analysis in this paper shows that our approach exhibits very advanced security, accuracy, precision, and low-energy trade-off. For comparable precision, our proposal outstands related clock synchronization protocols in energy efficiency and risk of attacks. These results are based on computations. 2011-04-07T17:31:15Z http://hdl.handle.net/2117/11217 Title: Energy-efficiency analysis of a distributed queuing medium access control protocol for biomedical wireless sensor networks in saturation conditions Authors: Otal Ruiz, Begoña; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos 2011-01-26T13:38:14Z http://hdl.handle.net/2117/10378 Title: Performance analysis of a cluster-based MAC protocol for wireless ad hoc networks Authors: Alonso Zárate, Jesús; Kartsakli, Elli; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos 2010-11-23T16:09:31Z http://hdl.handle.net/2117/10377 Title: Design and analysis of an energy-saving distributed MAC mechanism for wireless body sensor networks Authors: Otal Ruiz, Begoña; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos 2010-11-23T14:46:21Z http://hdl.handle.net/2117/10315 Title: Performance analysis of a persistent relay carrier sensing multiple access protocol Authors: Alonso Zárate, Luis Gonzaga; Alonso Zárate, Luis Gonzaga; Verikoukis, Christos 2010-11-16T15:05:14Z