Sebastian Max

IEEE 802.11s - Mesh Deterministic Access

In 2003, interests in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 Working Group (WG) led to formation of Task Group (TG) ldquoSrdquo. 802.11s develops an amendment for wireless local area network (WLAN) mesh. Unlike existing WLAN mesh products, 802.11s forms a transparent 802 broadcast domain that supports any higher layer protocols. Therefore, 802.11s provides frame forwarding and path selection at layer-2. While traditional WLANs are access point (AP) centered, the WLAN mesh is fully distributed. Hence, 802.11s considers extensions to the medium access control (MAC) too. The current draft 2.0 of 802.11s denotes the optional MAC as mesh deterministic access (MDA). Due to the high amount of indirect neighbors in a WLAN mesh, the current single-hop medium access control mechanisms cannot operate efficiently. In contrast, unlike traditional listen-before-talk scheme MDApsilas advanced medium reservation scheme allows for operation free of collisions. Therefore, MDA enables support for quality of service (QoS) and provides more capacity in the WLAN mesh. In this paper, the authors, who have contributed to the standardization of 802.11s since 2003, give insight to the basics of draft 2.0 of 802.11s and its principles. Furthermore, we provide detailed simulation results of 802.11psilas first WLAN mesh aware MAC: MDA. Our simulation results show that unlike the traditional enhanced distributed channel access (EDCA), MDA does not stall when the offered traffic is high. Due to its planned medium access, limited packet delay can be achieved.

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.

IEEE 802.11s MAC Fundamentals

The tremendous success of the Institute of Electronics and Electrical Engineering (IEEE) 802.11 wireless local area network (WLAN) standard led to severe competition. Due to Wi-Fi Alliance (WFA)s marketing, 802.11 became a universal solution for wireless connectivity. However, still a WLAN depends on wired infrastructure that interconnects the central access points (APs). To become independent of backbone networks leading to cheap deployments, the traditional single-hop approach needs to be replaced by wireless mesh networks (WMNs). Since several years, the research community develops routing protocols designed for wireless multi-hop networks. With 802.11s an integrated WMN approach is under development that adds the necessary functionality for interworking, security and routing. As its medium access control (MAC), 802.11s relies on the existing schemes. However, the current 802.11 MAC has been designed for wireless single-hop networks. Its application to WMNs leads to low performance. The capacity of the wireless medium can hardly be exploited. Thus, 802.11s provides an optional MAC that has been specifically designed for WMN. In this paper we explain the fundamental operation of the 802.11s MAC, explain its extensions and provide detailed simulation results on their performance.

Mesh technology enabling ubiquitous wireless networks: invited paper

Todays wireless networking technology provides high data rates. With IEEE 802.11n products, data rates beyond 500Mb/s are soon feasible for Wireless Local Area Network (WLAN). Due to a standstill in standardization the project IEEE 802.15.3a it was disbanded in 2006. Companies are pushing therefore their own solutions to the Wireless Personal Area Network (WPAN) market. Shortly, 480Mb/s will be available for WPAN applications. For large scale networks, IEEE 802.16 (aka Worldwide Interoperability for Microwave Access (WiMAX)) offers a solution for the Wireless Metropolitan Area Network (WMAN) market. Besides point-to-point connections, IEEE 802.16e supports mobile connections too. With recent development, wireless technology for ubiquitous connections is available in the market. Sensitive Modulation and Coding Schemes (MCSs), Multiple Input/Multiple Output (MIMO) and other new Physical Layer (PHY) technologies provide high data rates. However, upcoming wireless technology does not increase coverage. Like preceding standards, highest data rate is only available for short range communication. Therefore, supply of large areas with high speed connections demands dense installation of backbone connected devices. While Capital Expenditure (CAPEX) for hardware is low, deployment is expensive. The Operational Expenditure (OPEX) of wired and fiber optic networks is high. Furthermore they are not as widely deployed as needed for dense installation of connection points to the core network. Hence, rollout of high speed wireless networks is delayed until a solution is provided. Relay based deployment and Mesh topology for wireless networks helps to overcome the cost barrier. With this meshing functionality, wireless networks of the IEEE 802 standard family are a promising low-cost alternative to cellular Third-Generation (3G) networks In this paper we provide insight to current activities of Institute of Electronics and Electrical Engineering (IEEE) Working Groups (WGs) regarding Mesh technology. Furthermore we show possibilities and limitations of Wireless Mesh Networks (WMNs).

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.

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.

OFDM-UWB Physical Layer Emulation for Event-Based MAC Simulation

Simulation is one possibility to assess the performance of new medium access protocols for wireless communications. While the new algorithms are usually implemented in a very realistic way, the physical layer is emulated as a simple model. Often, this simplification is invalid in complex scenarios, where interference and non line of sight conditions degrade the signal quality. A complete physical layer implementation including the error correction, modulation, channel equalization and different channel pulse responses is not feasible in a layer two simulator. Hence, its characteristic is mapped onto a computational efficient stochastical model. The presented method differs from other error models in the way it is enriched with data to compute the packet error rates: The physical layer under examination, the WiMedia OFDM ultra wideband physical layer, is simulated in a detailed physical simulator and the error rates are derived then using an error analysis

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.

Transmit Power Control in Wireless Mesh Networks Considered Harmful

A Wireless Mesh Network (WMN) serves to extend the coverage of Access Points (APs) by means of Relay Nodes (RNs) that forward data between Mobile Nodes (MNs) and an AP. This concept reduces deployment costs by exchanging the wires between APs by a wireless backbone. Unfortunately, this also reduces capacity, owing to multiple transmissions of the same data packet on its multi-hop route.Hence, different mechanisms to increase the capacity of WMNs are investigated, one of them being transmit power control. By limiting the transmission power, interference on other links is reduced. As a consequence, it should be possible for them to use more susceptible and thus higher rate Modulation- and Coding Schemes (MCSs), which improves the system capacity.Unfortunately, the reduction of the transmission power has also the effect that the received signal power is reduced, which then requires more robust (lower-rate)MCSs, reducing capacity.In this paper, we use an analytical framework to compute the upper capacity bound of Wireless Mesh Networks(WMNs) with and without transmit power control. The comparison shows that the negative influence of the power control dominates the positive.