Deployment of Wireless Mesh Networks

In a previous blog post describing the basic components of a WMN, we highlight  that the  network performance depends mainly on the design issue. In what follows we will detail how to deal with the deployment of WMN in general and specially in the case of the Carmesh project. This latter problem  consists mainly of treating the two following problems:

• Where the mesh routers have to be placed?
• How to connect the mesh routers among them to form a balanced backbone topology?

First, the mesh nodes placement problem is related to the access tier design issue, which aims at achieving the following objectives:

1. Minimizing the installation cost: This objective can be achieved by reducing the number of mesh routers necessary to provide the target wireless coverage.
2. Coverage optimization: The mesh router positions are determined based on available maps or drawings and according to the required quality of service expressed in terms of Signal to Interference Noise Ratio (SINR).
3. Minimize the interference effect: To fulfil this objective, we have to ensure that the frequency channels assigned to the access radio interfaces are orthogonal (or sufficiently non-intereferring) to ultimately increase the nominal data rate for each user.

Second, the mesh nodes logical connections strategy deals with forming the backhaul network and its objectives can be summarized as follows:

1. Backhaul network connectivity: Selecting the links connecting mesh routers among them.
2. Maximizing the backhaul network capacity: Exploiting the overall backhaul network capacity.

The access network design problem can be solved first using the set covering problem to determine the minimum number of mesh routers required to cover all users. The coverage criterion is expressed as the signal strength assessed by each user to be higher than a certain predefined value, which offers a minimal nominal throughput. Once the positioning problem is solved, it is then necessary to assign a frequency channel to each mesh router (i.e. access radio interface) in order to communicate with its associated users. In IEEE 802.11-based WLAN, the channel assignment problem consists of assigning radio channels to mesh radio interfaces in such a way that the inter-channel spacing between close mesh routers is maximized. This minimizes  interferences and thus increase the wireless mesh overall network capacity.

However, the problem of backhaul network design can be solved by interconnecting the set of positioned mesh routers among them. The objective here is to select a set of links among all potential links, that allow to connect each mesh router to the gateway. The choice of links to keep has to be done with respect of certain constraints such as the limited number of radio interface, the ripple effect and channel dependency.

The deployment of WMN network is a hard problem and its complexity can not be managed easily even when we tackle with an orderly number of steps. This complexity has lead researchers to propose heuristics in order to deal with the complexity of the  aforementioned multiobjective problems. The optimal deployment of WMN allows to improve the network performance, it is a necessary phase in the design of WMN but not sufficient due to the shared nature of the wireless medium. Thus, the network dimensioning and capacity assignment are other important issues to deal with when designing and deploying wireless mesh networks.

Connected Car Rentals – how the Connected Car will change the Car Rental sector

In a previous post, we described how we see the used car market changing as the Connected Car evolves. Here, we focus on the Car Rental sector with particular emphasis on how data collection can impact the sector. (Note that while we focus on the power of the data here, we do view the Connected Car as offering more – see our vision post for details).

The car rental sector is very interesting from a Connected Car point of view from two particular perspectives. Firstly, the Connected Car sector is comprised of quite a few big organizations who can roll out Connected Car technology across their entire fleet quite easily. Secondly, the car rental sector is seeing some disruption with peer-to-peer solutions offering lower cost services – the Connected Car fits neatly into this paradigm shift. Both of these perspectives are examined a little further below.

Unexplained packet losses in NS-3: Where is my packet?

The NS-3 simulator tries to mimic as close as possible the journey of a packet through the IP-stack’s layers. Passing the packet from one layer to the next one is done through Callbacks or functions which access the packet. In this way, NS-3’s callbacks are taking successively control over the packet, which remains static.

How the Connected Car will change the Used Car Market

One of the things that the emerging world of big data will make possible is to know detailed history on everything. This will have profound impacts on selling ‘pre-loved’ items in general and used cars in particular. With the US used car market valued at around $400bn annually, this is worth noting.

Today, the used car market is – naturally – keen to know the history of the car. However, the way in which this is communicated is still quite limited: in some places a log book containing service history is the norm, other more sophisticated variants include carfax, which tracks odometer readings and reported crashes or, for example, the national database in Sweden which makes information on a car’s annual inspection available. While these do capture some key points in the story of the car, obviously having the full story rather than a set of snapshots can give a more comprehensive view.