**2. Rural community mesh network: A case of Peebles valley mesh in South Africa**

Peebles valley mesh (PVM) is a typical rural community mesh network that is funded by the International Development Research Centre (IDRC) and is deployed in Mpumalanga province in South Africa (Johnson, 2007). The conventional PVM network, consists of nine (9) single radio nodes, and covers an area of about 15 square kilometres in Masoyi tribal land. The Masoyi tribal land is located at the North East of White River along the road to the Kruger National Park in South Africa. The land is hilly with some large granite outcrops and it has a valley that stretches from the AIDS care training and support (ACTS) clinic and divides the wealthy commercial farms from the poorer Masoyi tribal area. The Masoyi community is underserviced with lack of tarmac roads and most houses are lacking running water. However, there is unreliable electricity present in the Masoyi area. The power outages occur on average one outage in seven days and might even last up to a full day (i.e., 24 hours). Albeit the government subsidizes the cost of electricity, a large population cannot afford electricity fees due to the low economic levels of the area. ACTS clinic (a nongovernmental organization sponsored clinic) provides medical services to AIDS patients, counseling, testing and Anti-retroviral (ARV) treatment (Johnson & Roux, 2008).

Figure 4 demonstrates architecture of the PVM network when HPNs are deployed. In this figure, the clinic connects to surrounding schools, homes, farms and other clinic infrastructure through a mesh network. The network is seen as community asset with some of the equipment at key nodes are actually belonging to the community. In this area mesh connectivity offers:

	- Auto-organizable connectivity against severe climatic conditions that commonly cause links, nodes, and network failures in the area.

Achievable Capacity Limit of High Performance Nodes for Wireless Mesh Networks 155

servers, personal computers as the mesh clients and HPNs may be installed to serve as wireless routers that link ACTS clinic accommodation flats to USAID offices about 1 Km away. The HPN link can connect Legogote Hospice and USAID premises about 3.35 Km over the valley via the Nurse house. The link over the valley between the USAID and Sakhile high school is about 2.4 Km. The link from Sakhile high school to the Legogote Hospice is about 4.6 Km, and the distance from high school to the farmers' houses is about 5.55 Km over the Peebles valley. It is also anticipated that the mesh network will expand to public clinics and schools that are farther way even up to 25 Km from the ACTS clinic center in the near future. In conclusion the rural PVM project has triggered further insights for newer research, development and innovation. The terrain irregularity, the long distances, the tree foliage coupled with the need for high capacity Internet provision in rural communities are the key drivers for the BB4allTM connectivity solution. It is also noted that clear understanding of classical physical channel models combined with innovative ICT products is expected to promote sustainable internet services to billions including previously disadvantaged subscribers

**3. Achievable capacity limit for a single link with multipath fading** 

In order to realize long distance coverages by single links with multipath effects in wireless mesh networks in rural areas, the IEEE 802.11a and IEEE 802.11n standards commodity devices can be used. This is because these devices are off-the-shelves, operate in multiple ISM channel bands and are affordable to the rural communities (Kyansanur & Vaidya, 2004). That is to say that only fewer radio interface cards at each node are needed than the number of non-overlapping frequency channels freely available. Kyasanur and Vaidya emphasized how expensive it could be to equip a node with one interface card for each frequency channel. The IEEE 802.11a standard, for example, offers 24+ non-overlapping channels and configuring a commensurate number of radio interface cards on each node might be unnecessary costly. As a result, many IEEE 802.11 interface cards can be switched from one channel to another, albeit at the cost of a switching delay. Moreover, the advantage of eliminating frame losses due to path-dependent (e.g., multipath fading effects), locationdependent (e.g., noise effects), and statistically independence between different receiving radios can be achieved by using multi-radio diversity principle (Miu, Balakrishnan & Koksal, 2007). The idea is that even when each individual reception of a data frame is erroneous, it might still be possible to combine the different versions to recover the correct version of the frame. In this study, the question to be addressed is that what is the capacity expression for single links with multipath effects in a rural based wireless mesh network. It is understood that most of previous studies solve capacity problem with simple channel models that may not reflect the true wireless channel conditions (Gupta & Kumar, 2000).

The standard IEEE 802.11a specifies an over-the-air interface between two wireless routers or between a wireless client and a router. It provides up to 54 Mbps in the 5 GHz frequency band and uses an orthogonal frequency division multiplexing (OFDM) encoding scheme.

(Mekuria et al., 2012).

**3.1. IEEE 802.11a air interface** 

<sup>(</sup>Source: *http://wirelessafrica.meraka.org.za/*)

Traditionally, the PVM is endowed with VSAT link that provides the network at the clinic with 2 Gbits per month at a download rate of 256 kbps and an upload rate of 64 kbps (Johnson & Roux 2008). The clinic provides 400 Mbps per month available to the single radio mesh network. The single radio mesh has nine users (mesh routers) so that each user (mesh router) receives about 44.4 Mbps per month on average. This traffic bandwidth drops downstream the network from the satellite gateway to the terminal users. This is due to lack of single radio network resiliency against effects of wireless multipath. However, in this document we believe that the design of the HPNs making the BB4allTM architecture can be a suitable candidate for improved capacity in multipath environment (BelAir Networks, 2006). As a result high data rates as the network scales away from the satellite gateway can be realized in the PVM deployment. The HPNs utilize the multiplicity of the low cost radio devices and non-overlapping channels to improve capacity delivered across the network.

Thus, the BB4allTM architecture constitutes a gateway connected to the internet via Sentech VSAT to the Peebles valley or ACTS clinic. Within the ACTS clinic there can be mesh

**Figure 4.** Mesh network architecture at Peebles valley in South Africa

servers, personal computers as the mesh clients and HPNs may be installed to serve as wireless routers that link ACTS clinic accommodation flats to USAID offices about 1 Km away. The HPN link can connect Legogote Hospice and USAID premises about 3.35 Km over the valley via the Nurse house. The link over the valley between the USAID and Sakhile high school is about 2.4 Km. The link from Sakhile high school to the Legogote Hospice is about 4.6 Km, and the distance from high school to the farmers' houses is about 5.55 Km over the Peebles valley. It is also anticipated that the mesh network will expand to public clinics and schools that are farther way even up to 25 Km from the ACTS clinic center in the near future.

In conclusion the rural PVM project has triggered further insights for newer research, development and innovation. The terrain irregularity, the long distances, the tree foliage coupled with the need for high capacity Internet provision in rural communities are the key drivers for the BB4allTM connectivity solution. It is also noted that clear understanding of classical physical channel models combined with innovative ICT products is expected to promote sustainable internet services to billions including previously disadvantaged subscribers (Mekuria et al., 2012).
