Summary of wireless multi-hop mesh networks
The technology of wireless networks is developing fast, and the applications of wireless
networks offer the publics and society much convenience. But, at present the traditional wireless
net is just used to replace the cable simply.
Ⅰ. Traditional WLAN
Along with the expanding of the wireless net’s scale, the requiring of wired connection for
each access-point in WLAN makes it meet a lot of challenges and in convenience in the
environment of lack of cable infrastructure. The traditional WLAN shows it’s insufficient
gradually.
The disadvantages of traditional WLAN:
a. The poor reliability:
In the traditional WLAN, several users get access to the wireless net through one
access-point directly—it is call “single-hop” networks. So long as one stoppage can breakdown
the whole networks.
Figure1. Traditional WLAN
b. The small coverage:
The normal technology of “point-to-point” or “point-to-multipoint” uses the short networks,
with the limitations of coverage, just like networks of 802.11 and Bluetooth.
c. The poor scalability:
As the joining and sharing data flow of access-points of extra nodes, the bandwidth of
whole networks will come down gradually.
d. The bad quality of communication:
Because of noise in link and mistakes in communication, the bandwidth will decrease as the
distance’s increasing. Most kind of wireless networks have “blind points” in its effective distance,
in which it shows the poor signal quality.
Ⅱ. The concept of wireless mesh network (WMN)
With the evolution of communication technique and catering to the need of the market, a
new wireless network emerges, which is called “wireless mesh network”, short for “WMN”.
Wireless mesh network is a flexible communication system to improve the efficiency and quality
in single transmission. WMNs have emerged as a cost-effective alternative for large-area
communications. WMNs have also become an important technology for constructing wireless
networks beyond the 3G high-speed cell phone networks. A mesh network is an ad hoc network
that employs one of two connection arrangements: full mesh topology or partial mesh topology.
WMNs do not require wired infrastructure for long-haul communications, thus offering the
major benefit of low-cost and flexible deployment and maintenance. WMNs, however, suffer from
the same security vulnerabilities as conventional wireless networks. Because data are transmitted
in the form of radio waves in the air without physical boundaries, packet eavesdropping and
packet intercepting can be carried out easily by attackers with the help of relatively cheap
equipment. Moreover, wireless channels may be disturbed by noise and interference, which affect
the quality of communications. WMNs are multi-hop networks, which are especially vulnerable to
interference problems: Adjacent hops on the same path and neighboring paths could interference
with each other. WMNs are distributed networks, which have additional issues on routing,
authentication, and key management. Therefore, security is a major concern in WMNs.
Ⅲ. Ad hoc networks and Wireless mesh networks
Figure2. Ad hoc network
a. Ad hoc networks
Ad hoc networks are wireless networks that can be deployed quickly. A mobile ad hoc
network is a potential solution for deploying a data and voice network for FRs in scenarios with
limited or no infrastructure. All nodes in the network act as equal peers as Figure 2. An ad hoc
network typically uses a suitable routing protocol such as AODV or DSR to allow multi-hop
communication between the nodes. One or more nodes may act as gateways and connect the ad
hoc network with the Internet or some other network. The gateways may use a wired or even a
wireless back-haul to exchange data with an external network. Self-contained ad hoc networks
may not even have a back-haul. Ad hoc networks generally have only single-radio nodes and can
be considered to be single-tier mesh networks.
b. Wireless mesh networks
In the full mesh topology, each node is connected directly to each other node. In the partial
mesh topology, nodes are connected to only some, but not all the other nodes. Wireless mesh
networks thus combine a mesh topology with ad hoc wireless network characteristics. Mesh
networks can be built on a mix of fixed and mobile nodes interconnected via wireless links to form
a multi-hop ad hoc network.
Figure3. Wireless multi-hop mesh network of two tiers
In a sufficiently dense wireless mesh network, there is rarely a single point of failure and the
network is able to recover from the failure of an individual node by routing around it to other
nodes in a direct or multi-hop manner. A mesh network allows nodes to communicate with other
nodes without being routed through a central switch point, thus eliminating centralized failure and
providing self-healing and self-organization behavior. As shown in Figure 3, several mesh routers
act as APs to the mobile clients. The mesh provides a wireless infrastructure to mobile clients
using an ad hoc wireless back-bone to route packets to their respective destinations. One or more
