Erik Weiss

Analysis ofWiMedia-based UWB Mesh Networks

Regarding maximum transmission rates, Ultra Wideband (UWB) seems to be the wireless technology which could successfully replace most of the data-cables in office and home environments: With up to 480 Mb/s gross data rate, wireless high-definition video streaming and data synchronization become feasible. Of course, these advantages come at a price: UWB is designed for short-range communication, limited to 10 m. While this suffices for some application, it does not fulfill the vision of ubiquitous wireless access in the fully-connected home. A straightforward solution to increase the network coverage is given by Wireless Mesh Networks (WMNs). In this paper, we analyze if the combination of UWB and WMN is able to provide the required coverage and the expected data rates. Several different deployment concepts (including ad- hoc networking and dedicated mesh relays) are evaluated with a realistic system model, which is able to compute the resulting network capacity. The results show that under the assumptions of the model, i. e. a MAC which is able to exploit spatial divided frequency reuse, UWB mesh networks are able to provide a stable capacity of more than 100 Mb/s in a typical scenario of up to 250 m2. Hence, the combination of the two technologies is able to succeed in much more application scenarios in comparison to the current UWB standard.

Performance analysis of temporally ordered routing algorithm based on IEEE 802.11a

This paper presents a performance analysis of the temporally ordered routing algorithm (TORA) protocol on top of IEEE 802.11a. IEEE 802.11a offers up to eight different coding schemes. Depending on the coding schemes the ad hoc routing behaviour differs. This paper describes the influence of the coding schemes, reviews the TORA protocol including the link reversal algorithm and presents the combined results. This research focuses on the application of TORA in a scenario where an ad hoc network is connected to the Internet using an ad hoc gateway. Special emphasis was spent to a separated investigation of the protocol performance for uplink and downlink routes. The paper presents three enhancements to TORA avoiding and finding loops. Simulation results are presented showing the performance of TORA on top of IEEE 802.11a and describing the feasibility of TORA to be used as routing protocol in ad hoc integration scenarios.

Avoiding route breakage in ad hoc networks using link prediction

This paper presents a new concept to improve ad hoc routing protocols exploiting IEEE 802.11a link adaptation information. The IEEE 802.11a link adaptation information is used to predict the link stability and link lifetime. After introducing he IEEE 802.11a MAC layer information and its transmission nodes, the paper reviews some insights of the IEEE 802.11a link adaptation behaviour. Based on the link layer information, new route maintenance protocols ERRA (early route rearrangement) and ERU (early route update) are proposed to improve the active route maintenance in ad hoc networks.

Relay-based vs. Conventional Wireless Networks: Capacity and Spectrum Efficiency

Conventional radio cells suffer from the disadvantageous distribution of the transmission rates. High transmission rates are only available in the close vicinity of the access point, whereas the distribution of mobile stations behaves complementary. Hence, the provided capacity of the access point is only partly used and the majority is wasted. This drawback will grow with the introduction of future transmission techniques, which increase the maximum transmission rates available at short distances. Therefore, it is unlikely that the traditional design of cellular radio systems can achieve the ambitious throughput and coverage requirements of fourth- generation (4G) radio networks. We propose to extend conventional multi-cellular systems by applying relay-enhanced topologies to each cell. To encourage this evolutionary step we present an analytical model to compute the upper bound capacity and the spectrum efficiency of wireless networks. Based on this analytical model the potential of conventional cellular systems is compared with relay-enhanced networks.

Opportunistic Wireless Internet Access in Vehicular Environments Using Enhanced WAVE Devices

In this paper we study the feasibility of providing automotive users the Internet access using C2C communication with help of roadside infrastructure and the novel Vehicular Communication Gateways (VCG), which is developed in the MYCAREVENT project. A technical solution of managing the opportunistic wireless links between On-Board Units (OB Us) and Road-Side Units (RSUs), as well as between OB Us and VCGs, is developed based on WA VE system. To further enhance the performance of WA VE system concerning IP traffic in highly dynamic vehicular environments we propose a link status aware MAC queue architecture. Stochastic simulation results are presented to prove the concepts and validate the proposed solutions.

Improving routing performance in wireless ad hoc networks using cross-layer interactions

This article presents a combined layer two and three control loop, which allows prediction of link breakage in wireless ad hoc networks. The method monitors the physical layer transmission mode on layer two and exploits the gained knowledge at layer three. The mechanism bases on link adaptation, which is used in IEEE 802.11a WLAN to select the transmission mode according to the link quality. The process of link adaptation contains information that is useful to predict link stability and link lifetime. After introducing the IEEE 802.11a Medium Access Control (MAC) and PHY layer, we present insight to the IEEE 802.11a link adaptation behaviour in multi-hop ad hoc networks. The link adaptation algorithm presented here is derived from Auto Rate Fallback (ARF) algorithm. We survey the performance gain of two newly developed route adaptation approaches exploding the prediction results. One approach is Early Route ReArrangement (ERRA) that starts a route reconstruction procedure before link breakage. Hence, an alternative route is available before connectivity is lost. Early Route Update (ERU) is a complementing approach that enhances this process, by communications among routing nodes surrounding the breaking link. The delay caused by route reconstruction can be significantly reduced if prediction and either of our new route discovery processes is used.

Spectrum sharing in IEEE 802.11s wireless mesh networks

With current amendments, transmission rates of 100Mb/s and more become possible with IEEE 802.11 WLANs. On the one hand, this allows the end user to change from wired to wireless infrastructure in even more application scenarios; on the other hand interference sensitive modes reduce the maximum range between the mobile station and the access point (AP). To extend the transmission range transparently, relay APs form a mesh network and provide wireless connection over large areas. Besides path selection, a crucial capability of a wireless mesh network is the ability to share the available spectrum among the participants. In this work, we classify two inherently different MAC protocols according to this ability. The well-known IEEE 802.11 DCF takes the position of a typical CSMA/CA protocol, whereas the Mesh Network Alliance (MNA) represents a distributed, reservation-based approach. To assess their performance, we follow a dual approach: first we develop a method to compute the capacity bounds of the protocols in the considered scenarios. It helps to estimate the absolute gain of spectrum sharing in wireless mesh networks. Second, the WARP2 simulation engine is used to compare the distributed behaviour of both protocols. This results in a relative evaluation. A final conclusion is drawn by combining the simulation and the theoretical results. It underlines the significant possibilities of the MNA approach and shows future directions for capacity gains.

Benefits and limitations of spatial reuse in wireless mesh networks

Local area wireless networks are based on the cell topology: Clients associate to one of several access points, which are connected using a wired backbone. As high data rates are only available close to the access points, a dense infrastructure is needed. This results in high costs, especially for the installation of the wired backbone. A wireless mesh network can be used to reduce the deployment costs by connecting only few access points to the backbone; mesh nodes extend the coverage by forwarding data over wireless hops. Since the wireless medium has to be shared by the nodes, multi-hop traffic requires a high capacity. Hence, mechanisms which increase the system capacity in wireless mesh networks are needed. In this paper, we rate how much capacity can be gained by the introduction of spatial reuse. First, a system model of the wireless network is presented. This model includes a stochastic channel behavior and the signal strength/SINR requirements of a link. Additionally, the possibility of link adaption is incorporated. As the exact calculation of the system capacity using this model is NP-hard, we develop and survey heuristics that reduce the complexity. Then, we apply the developed algorithms to evaluate different spatial reuse strategies. An upper bound is given by a network controlled by a omniscient scheduling entity; a lower bound is provided by refraining from spatial reuse. The results show that under the assumptions of the models at least a capacity increase by a factor of two is feasible; under optimal conditions a 12-fold increase is possible.

Capacity bounds of deployment concepts for Wireless Mesh Networks

Local area wireless networks are like cellular systems: Stations associate to one out of several access points (APs), which connect to a wired backbone. Due to signal attenuation and transmission power limitations, radio connectivity is available only sufficiently close to an AP. In scenarios with a dense deployment of APs the wired backbone causes unprofitably high costs. A Wireless Mesh Network (WMN) serves to extend the coverage of APs by means of Mesh Points (MPs) that forward data between a station and an AP. This concept reduces deployment costs, but reduces also network capacity, owing to multiple transmissions of the same data packet on its multi-hop route. This paper analyzes how the capacity of cost-limited WMNs can be optimized. A layered model of a WMN specifying the typical characteristics of the network is used to calculate the upper capacity bound. Based on the heuristics developed, networks of more than 150 nodes (APs, MPs and stations) can be handled. We apply the method to investigate the combination of three measures for improving the WMN capacity: (i) concurrent scheduling of transmissions, (ii) application of directional antennas and (iii) variable number of MPs per AP. The capacity bounds for different combinations of the measures mentioned is computed and compared. Combined with a simple cost model, these results are useful to provide insight into the economical feasibility of WMNs for wireless Internet access.

Frame descriptor tables for minimized signaling overhead in beyond 3G MAC protocols

In this paper we assess the performance of the frame descriptor tables (FDT) concept applied in combination with a highly dynamic resource allocation scheme. Beyond 3G (B3G) medium access control protocols (MAC) have to meet challenging requirements. In order to support the need for quality of service (QoS) and considering the scarce availability of radio resources, B3G MAC protocols must implement an intelligent resource allocation strategy with minimum signaling overhead guaranteeing high spectral efficiency. In this context the FDT concept seems to be a promising candidate. By eliminating redundant description of frame contents across frames the concept helps to reduce signaling overhead in a frame based reservation scheme. To keep as much flexibility as needed it seems reasonable to apply the FDT concept in combination with a highly dynamic resource allocation scheme. Simulations done in the course of this work prove the high quality of this combined approach