Excellent explanation of the combination of Wireless Mesh Network and writing Relay Technology

The wireless mesh network is comparable to a small-sized Internet, which can better play a wireless role in enterprises. Then, the wireless mesh network is also combined with other technologies to play a more powerful role. The following is a detailed description of the knowledge of Wireless Mesh Network + cooperative relay technology.

Combination of Wireless Mesh Network and cooperative Relay Technology

1. The backbone network needs to implement a wireless Mesh Structure

The Wireless Mesh Network is a wireless network technology based on the IP protocol. In terms of the network topology, the wireless mesh network can be seen as a wireless and micro-version Internet. With the development of broadband wireless technology, people need Wireless Networks with higher data rate, higher spectrum efficiency, higher coverage and stronger business support capabilities. For example, B3G/4G requires a transmission rate of 1 Gb/s, the required spectrum must be at least 100 MHz. It is difficult to find such broadband spectrum requirements in the existing frequency band. Therefore, we need to allocate a higher B3G/4G frequency band, such as 5 GHz or 6 GHz.

Increasing the working frequency and bandwidth are conducive to increasing the data rate. However, increasing the frequency will narrow the coverage of the residential area, leading to conflicts between the data rate and coverage, A compromise between data rate and coverage is required. For example, IEEE 802.11n expects that the data rate of the Media Access Control (MAC) layer will reach 100 Mb/s within the 15 m range; ultra-wideband (ultra-wideband) can provide a data rate of up to 480 Mb/s, however, the coverage can only reach 2 m or even lower. In this case, to achieve a high data rate within a large range of coverage, a large number of APS will be required for future wireless networks. However, it is difficult to install and deploy a large number of APs. On the one hand, the construction cost is too high, and on the other hand, it is not realistic to connect all wireless aps to the wired backbone network, especially in regions that do not currently have wired services.
 

Although the Mesh-based and relay-based structure is a feasible solution, many wireless Mesh products on the market can work with WPAN) WMAN, WLAN, and WBA systems. However, if the whole wireless Mesh network is regarded as a ocean, these WPAN, WMAN, WLAN, and WBA are like isolated islands in the ocean. Their central controllers can provide users with real services only after they are connected to the backbone network. Therefore, from this perspective, to achieve full-network wireless Mesh coverage, the first thing to solve is the wireless implementation problem of the backbone network [10].

2. Structure of the Wireless Mesh Network

A wireless mesh network uses a multi-hop wireless network, and data streams are sent to and from the wired Internet gateway. Compared with flat Ad hoc, the wireless Mesh network features a layered structure, and its nodes can be divided into Mesh routers and Mesh clients based on their functions. These Mesh nodes can form a full Mesh structure or a part of the Mesh structure. The full Mesh structure means that any two nodes in the network can be directly connected, and some Mesh structures mean that only some nodes in the network can communicate directly.

A Mesh router not only provides routing functions, but also provides gateway or bridge functions. Compared with traditional wireless routers, a wireless Mesh router can achieve the same coverage with a low transmission power through a multi-hop Network. By strengthening the MAC protocol in the Mesh router, it can also make it more scalable in a multi-hop Mesh network environment. The Mesh client must have the networking function and can also be used as a router. However, the Mesh client does not have a gateway or bridge concept, and a Mesh client has only one wireless interface and can only support one wireless access technology.

Currently, the Mesh router and Mesh client can form two basic wireless Mesh structures: the infrastructure Wireless Mesh Network and the client Mesh network. But what is promising is the hybrid structure of the two. This Wireless Mesh Network is a combination of the Infrastructure structure and the client structure. The client can access the network through the Mesh router, and can also directly form a Mesh network with other Mesh clients.

3. Features of cooperative Relay Technology

Cooperative relay is also called cooperative diversity. Its principle comes from the concept of "virtual antenna array. Cooperative relay is an extension of single-path Relay. One or more nodes with common coverage areas can be introduced between the source node S and the target node D to act as the relay node R, the target node can merge data from the source node and from the relay node. In this way, the pressure on terminals that cannot be configured with more antennas can be mitigated [11]. Source nodes, relay nodes, and target nodes are acted by base stations (BS), relay stations (RS), and user terminals (UT.

According to the different sending and receiving time slots between each node, "X → Y" is defined to indicate X transmitting and Y receiving. Cooperative relay can be divided into three types as shown in Table 1. The target node merges signals received by different time slots to obtain the spatial diversity gain. Because the target node uses signal information from multiple paths, the space diversity gain can be obtained to ensure the data rate and reliability of the relay link.

4. Integration of wireless mesh domain cooperative Relay Technology

As we can see from the past, the wireless Mesh network mainly implements Mesh structure at the network layer or data link layer. However, the idea of cooperative relay is mainly embodied in the physical layer, to ensure the transmission speed and reliability of the wireless relay link. The fixed wireless Mesh network is used as an example to introduce the application of cooperative relay in the wireless Mesh network [12]. The Mesh nodes include AP, fixed/or nomadic RS. UT can be included in the Mesh structure, but it must be connected to the Mesh nodes in the Mesh structure to accept network services. AP can be either BS or RS, and can be directly connected to the backbone network (generally Internet ). Node C can merge signals from nodes A and B to implement cooperative relay and obtain spatial diversity gain.

Cooperative relay can be used in any wireless relay link. In addition, to fully utilize the spectrum resources and multi-input multi-output (MIMO) technology, multiple antennas can be configured in the source node, relay node, and target node to fully utilize the cooperation of different RS, it can implement cooperative MIMO relay at the target node, greatly improving the data rate of the wireless relay link. The simulation transmission rate is about twice higher than that of conventional MIMO. With the development of wireless technology, the adoption of cooperative MIMO Relay Technology in wireless mesh networks will certainly be a Development Direction [13].