The Spectrum Shortage Problem: Channel Assignment and Cognitive Networks

Recent studies have shown that the proliferation of wireless applications and services, experienced in the last decade, is leading to the challenging spectrum shortage problem. We provide a general overview regarding the spectrum shortage problem from the point of view of different technologies. First, we propose solutions based on multi-radio multi-channel wireless mesh networks in order to improve the usage of unlicensed wireless resources. Then, we move our focus on cognitive networks in order to analyze issues and solutions to opportunistically use licensed wireless resources. In wireless mesh networks, the spectrum shortage problem is addressed equipping each device with multiple radios which are turned on different orthogonal channels. We propose G-PaMeLA, which splits in local sub-problems the joint channel assignment and routing problem in multi-radio multi-channel wireless mesh networks. Results demonstrate that G-PaMeLA significantly improves network performance, in terms of packet loss and throughput fairness compared to algorithms in the literature. Unfortunately, even if orthogonal channels are used, wireless mesh networks result in what is called spectrum overcrowding. In order to address the spectrum overcrowding problem, careful analysis on spectrum frequencies has been conducted. These studies identified the possibility of transmitting on licensed channels, which are surprisingly underutilized. With the aim of addressing the resources problem using licensed channels, cognitive access and mesh networks have been developed. In cognitive access networks, we identify as the major problem the self-coexistence, which is the ability to access channels on a non-interfering basis with respect to licensed and unlicensed wireless devices. We propose two game theoretic frameworks which differentiate in having non-cooperative (NoRa) and cooperative (HeCtor) cognitive devices, respectively. Results show that HeCtor achieves higher throughput than NoRa but at the cost of higher computational complexity, which leads to a smaller throughput in cases where rapid changes occur in channels' occupancy. In contrast, NoRa attains the same throughput independent of the variability in channels' occupancy, hence cognitive devices adapt faster to such changes. In cognitive mesh networks, we analyze the coordination problem among cognitive devices because it is the major concern in implementing mesh networks in environments which change in time and space. We propose Connor, a clustering algorithm to address the coordination problem, which establishes common local control channels. Connor, in contrast with existing algorithms in the literature, does not require synchronization among cognitive mesh devices and allows a fast re-clustering when changes occur in channel's occupancy by licensed users. Results show that Connor performs better than existing algorithms in term of number of channels used for control purposes and time to reach and stay on stable configurations

Assessing the Performance of a MIMO SDR Testbed with Dual Transceiver Implementation

Software Defined Radio testbeds are becoming increasingly used in the wireless networking community, given their feature of leaving wireless network designer full control of the PHY layer. On the other hand, SDR testbeds are formed of very complex software/hardware tools, in which implementation bugs are likely and difficult to identify. For this reason, assessment of the results provided by an SDR platform should be a fundamental, preliminary step in the performance evaluation process. In this paper, we provide a thorough assessment of the MIMONet SDR platform for network-level exploitation of MIMO technology. To assess the platform, we have used two different implementations of an OFDM transceiver: one based on Matlab, the other on the GNU Radio software. We have then crossvalidated performance by means of extensive measurements using the two alternative implementations. We have also designed and implemented a fine grained SNR and BER estimation methodology, that allowed us to carefully validate performance of the two software implementations against theoretical predictions. When collectively considered, the results of our measurements promote MIMONet as the first SDR testbed with carefully validated performance

End-to-End Bandwidth Reservation in IEEE 802.16 Mesh Networks

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Bandwidth reservation in IEEE 802.16 wireless mesh networks

The need for broadband wireless access systems in residential and small-to-medium sized business environments is increasing due to their requirement for higher bandwidth network access. IEEE 802.16 is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL and includes a mesh mode operation where nodes cooperate to relay the users packets toward their destinations in a multi-hop fashion. The mesh mode does not include support to traffic flows with strict Quality of Service requirements. In this work, I propose an End-to-end Bandwidth Reservation Protocol (EBRP) in the backhaul of a Wireless Mesh Network using IEEE 802.16 mesh. Although EBRP shares the same conceptual rationale of most IP-based reservation protocols, such as RSVP, its distinctive feature is that it is carried out at the Medium Access Control (MAC) layer. EBRP exploit the control messages to solve the problem of providing traffic flows with strict real-time requirements through a end-to-end bandwidth reservation, which is integrated with the IEEE 802.16 MAC through the addition of some information elements to the MAC control messages. The messages that are used to establish traffic flows are conveyed as Information Elements (IEs) of Mesh Distributed Scheduling (MSH-DSCH) MAC control messages, which are advertised periodically by all nodes. The MSH-DSCH format has been modified so as to be still compliant with the IEEE 802.16 standard by using the fields that are reserved for future use. The framework includes a call admission control procedure which requires all the nodes to have complete knowledge of the network topology, which can be achieved by modifying existing routing protocols. EBRP allows the available resources to be allocated efficiently by exploiting technology-specific information available at the MAC. The main idea is to partition the data sub-frame into a number of groups of equal size. Each link of the network is then assigned to one of these groups in a distributed manner by all nodes so that all the links that belong to it can be activated simultaneously and any node of the network can allocate resources for one of its links independently of one another

End-to-End Bandwidth Reservation in IEEE 802.16 Mesh Networks

IEEE 802.16 mesh does not include support to traffic flows with strict Quality of Service requirements. In this paper, we propose an End-to-end Bandwidth Reservation Protocol (EBRP) in the backhaul of a Wireless Mesh Network using IEEE 802.16 mesh. The distinctive feature of EBRP is that it is carried out at the Medium Access Control (MAC) layer. Therefore, EBRP not only makes the resource reservation process extremely rapid, it also allows the available resources to be allocated efficiently by exploiting technology specific iinformation available at the MAC. We present EBRP as part of a framework which also includes the support for performing distributed Call Admission Control (CAC). Preliminary simulations results obtained with VoIP traffic and nodes arranged in a grid topology are presented to show the effectiveness of EBRP, with ideal CAC computation

A multi-element psychosocial intervention for early psychosis (GET UP PIANO TRIAL) conducted in a catchment area of 10 million inhabitants: study protocol for a pragmatic cluster randomized controlled trial

Multi-element interventions for first-episode psychosis (FEP) are promising, but have mostly been conducted in non-epidemiologically representative samples, thereby raising the risk of underestimating the complexities involved in treating FEP in 'real-world' services