Low cost data access system for Rural and Under-Served Areas

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by Nkokoba Peter Mailula

Co-Authors: Damien Chatelain (Supervisor), and Moremi Moemedi, French South African Technical Institute in Electronics (F’SATIE), Department of Electronic Engineering,

Tshwane University of Technology, P/Bag X680, PRETORIA, 0001

E-mails: Pmailula@csir.co.za, Dchatelain@fsatie.ac.za , Moremi.Moemedi@fsatie.ac.za

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Abstract: In this paper attention is focused on the challenges that rural and under-served areas in South Africa pose in the provision of telecommunication services. The aim is to provide access to information (data e.g., internet) to rural and under-served areas at an efficient and affordable cost. Available technologies and integration of currently emerging wireless local area networks (WLAN) that support IEEE 802.11b standard with the Internet are investigated. Configuration issues are discussed and technology set-up demonstrated. Measurements and simulation are performed to validate the suitability of deploying the technology in those areas.

Keywords: WLAN, Wi-Fi (Wireless Fidelity), Internet, Rural Areas, Under-Served Areas, Multi-User basis.

I. Introduction

The potential of Internet as a source of learning and information sharing has been widely used in all avenues in developing and developed countries. However, little attention is still given to the deployment of efficient and affordable telecommunications networks in some other sectors of the community. This lack of access prevents the population from being well informed about political and economic news, hence hindering the people from availing themselves to the benefits of distance education, telemedicine and other similar services.

In addition, economic development is also hampered because besides being a pool of knowledge acquisition and sharing, Internet is important in businesses development due to its ability to provide nationwide, regional and worldwide exposure to even small businesses at a reasonable cost.

Furthermore, in many developing countries, Internet access is billed on time and distance sensitive basis as opposed to flat usage fees. This, coupled with the relatively low per capita income in these countries inhibits Internet usage. Other factors negatively influencing internet demand are scarcity of computers and telephone lines, not being able to use English, the currently predominant language of the Internet, and generally low education and skills levels. The access problem is particularly acute in rural and under-served areas where not only computers and phone connections

are nonexistence, but also even electricity may not be available [1].

To achieve self-sustainable Internet service, in a rural and under-served setting, the Internet is likely for some time to be delivered as a community resource, rather than a personal one. In other words, each community might have shared resources that are financially sustained through some combination of user fees and outside revenue [2]. In this scenario, WLAN based on IEEE 802.11b standard using an existing Ethernet backbone is proposed as a possible solution to provide access to rural and under-served areas on a multi-user basis. In this study, the following could hold the key to some possible solutions [3]:

1. An approach of small entrepreneurs to provide Internet and voice services within their own communities by purchasing inexpensive basic radio equipment and transmitting on unlicensed frequencies.

2. Collections of these local operators, collaborating and interconnecting with larger Internet and basic service operators, begin to weave together a patchwork of universal access where little or no telecommunications services existed before.

3. This access patchwork should be cheap, robust, and extremely responsive to innovation ultimately ensuring revenue flow and creating value to the community.

II. Wi-Fi/WLAN- Wireless Fidelity/ Wireless Local Area Network

Wireless data networks (Wide Area Networks and Local Area Networks) based on the IEEE 802.11 or “Wi-Fi” standard are perhaps the most promising wireless technology. Given its popularity in developed nations, it is reasonable to consider the use of Wi-Fi in developing countries as well. The forces driving the standardization and proliferation of Wi-Fi in the developed world could also stimulate the communications market dynamic in the developing world [4]. Wi-Fi can easily be adopted as a possible solution for rural and under-served areas by virtue of the following: its ease of set-up, use, and maintenance; its relatively high bandwidth; and, most importantly, its relatively low cost for both users and providers. Standard Wi-Fi 802.11b operates in the

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unlicensed 2.4 GHz Industrial, Scientific, and Medical (ISM) frequency band and provides up to 11Mb/sec data rates over a 22 MHz passband. 802.11b utilizes DSSS (Direct Sequence Spread Spectrum), a modulation technique to allow a device to communicate at a higher rate by distributing its energy over a contiguous frequency band. It also uses the Media Access Control (MAC) protocol and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). In the 83.5 MHz frequency band there are fourteen 22 MHz wide sub-channels that the access point can use, of which three channels are non-overlapping. Current maximum transmitted power for this wireless device is 100 mW.

Bit Rate

Range

11Mb/s 5.5Mb/s 2Mb/s 1Mb/s

Open Office

160m 270m 400m 550m

Semi open office

50m 70m 90m 115m

Closed office

25m 35m 40m 50m

Table 1: Range/Bit Rate Comparison in different Office Environment [5]

Tests in rural settings show that a standard WiFi card (such as commonly used with laptop PCs) can provide good connectivity up to a ½ kilometer radius given line-of-sight. With the addition of high gain antennas and repeaters, it is possible to achieve point-to-point connectivity at distances of up to 25 kilometers. Wi-Fi access points (devices commonly used to provide a Wi-Fi network-Wireless Development Platform) currently retail at less than R6000.00 and Wi-Fi cards retail for under R1000.00 from Miro Network Distributors.

WiFi technology can be adopted as a viable technology for rural and under-served connectivity solutions to connect schools, clinics, library and community centers to each other and to the Internet. This will ultimately create sustainable business models and universal access to ICT in rural and under-served areas. However, the successful implementation of this technology and the choice of usage model are also guided by an intimate

knowledge of rural communities and their information- and communication-related needs [6].

III. Infrastructure and Architecture

The basic principle of WLAN operations resembles cellular networks –access point (AP) broadcast and receives over short distance (up to 100m) from users’ terminal, equipped with network interface cards (NIC). Base stations are connected to Ethernet network backbone, in turn connected to MAN, WAN or public Internet. The major benefit of such an architecture is that user’s experience of working in this wireless network resembles very much the work in wired environment – the speed of the network can be up to 11Mbps, keeping mobility, limited only by the range of AP reach. A concentrated geographic area where high-speed wireless LAN access is available is called ‘a hotspot’. In general, WLAN of popular standards can operate in two modes: peer-to-peer and client/access-point12. Both types of architecture offering fully distributed data connectivity.

IV. Peer- to-Peer Network Topology

Peer-to-peer is a WLAN in its most basic form. Two PCs equipped with wireless adapter cards form a simple peer-to-peer network, enabling the PCs to share resources. This type of network requires no administration or reconfiguration, but also bypasses the central server, inhibiting client/server sharing. This type of independent or ‘Ad Hoc’ wireless networking can be used for PCs communicating directly with each other. In such WLAN configuration, access points function as repeaters, which are used to increase the range of WLAN. Possible applications include: collaborative work groups; small/branch offices sharing resources; remote control of another PC; games for two or more players; demonstrations. It is important to note that at the moment peer-to-peer networks for public use are not widespread, however there are some research in this area. Vendors develop software, allowing deploying WLAN based on ‘ad hoc’ mode for public use [8].

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Figure 01: Peer-to-Peer WLAN Mode

V. Infrastructure

Client and Access Point: A Client and Access Point network allows for extended range capabilities; they are also able to benefit from server resources, as the AP is connected to the wired backbone. The number of users supported by this type of network varies by technology and by the nature and number of the transmissions involved. Generally, client and access point networks can support between 15 and 50 users.

Figure 02: Single Access Point Mode

Multiple Access Points: Although coverage ranges in size from product to product and by differing environments, WLAN systems are inherently scalable. As APs have limited range, large facilities such as warehouses and college campuses often find it necessary to install multiple access points, creating large access zones. APs, like cell sites in cellular telephony applications, support roaming and AP-to-AP handoff. Large facilities requiring multiple access points deploy them in much the same way as their cellular counterparts, creating overlapping cells for constant connectivity to the network. As network usage increases,

additional APs can be easily deployed. This type of architecture is the most popular to build WLANs for public use.

Figure 03: Multiple Access Point Mode

III. Results

A. Wi-Fi Design

A Wi-Fi Development platform is a router that can either be configured as point to point or point to multi point. In our case a client and a server has been configured in a laboratory environment. Firstly, a Client and Server were configured using static IP (Internet Protocol) addressing as is shown in figure 04 below. A LAN (Local Area Network) was connected to the WiFi platform (Access Point) at Net 0 with IP address 168.172.114.110. A Local PC connected to Net 1 at the WiFi platform with IP address 10.10.10.5 and 10.10.10.2 respectively. An IP address of 10.10.20.1 was then assigned to Wi 0. Again on the client side, Wi 0 was assigned with IP address of 10.10.30.1. At Net 0/sis 0 an IP address of 10.10.30.1 was assigned while the client PC was assigned with IP address of 10.10.30.2

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Figure 04: WiFi Development Platform and Addressing

Again, a laptop with an NIC (Network Interface Card) installed was configured using static IP addressing as is done on the peer-to-peer configuration. The wireless clients or laptop can move freely throughout the footprint of the AP. The Signal Strength and data rate proved to be very good few metres away from the AP as is shown in figure 05 below. Data rate reduces from 11Mbps, 5.5 Mbps, 2 Mbps and 1 Mbps as the distance increases. The signal strength also drops depending on the type of obstacle/clutter on the environment.

Figure 05: Wireless Network Connection Status

The number of simultaneous users that an access point can support depends mostly on the amount of data traffic at the time (heavy versus light downloads and uploads). Bandwidth is shared among users on a WLAN as with wired network connections. Network performance, as gauged by the number of simultaneous users, hinges on the combined computing activity. For example, in 802.11b, each hardware access point has up to 11 Mbps throughput. This capacity is adequate for: 50 nominal users who are mostly idle and check an

occasional text based e-mail. 25 mainstream users who use a lot of e-mail and

download or upload moderately sized files. 10 to 20 power users who are constantly on the

network and deal with large files.

To increase capacity, more access points may be added, which gives users more opportunity to enter a network. Networks are optimized when the access points are set to different channels. In theory, many users could then share up to 33 Mbps total capacity (although no single user would ever have throughput faster than 11 Mbps). In reality, clients associate with the access point with which they share the strongest signal, so the bandwidth may not be dispersed evenly among users [9]

B. Community Infrastructure Model

Figure 06: Model for WLAN (Wi-Fi) Network Infrastructure

C. WLAN Signal Strength Prediction Model/ Design Tool

Internet BackboneSchools

Library

Medical Centers

AccessPoint

Community Centers

Businesses

Access Point

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The WLAN design tool for the prediction of signal strength/ power at different distances away from the Transmitter (Access Point) can be used for the planning of the expected quality of the design before a practical layout is carried out [10]. The model is used to do the link budget, that is, how much power shall be available at the receiver after the signal has traveled over a stated distance. This model was chosen because it allows us to predict the signal over some distance, which will help in designing a cost-effective wireless local area network. Using this software, we were able to do simulations in an open office along the passage.

Figure 07: Link Budget Simulation Results

D. First Iteration Simulated and Experimental Results for Indoor testing

Figure 09: Comparison between Experimental Measurements and Simulated Results

This graph is a plot of predictions and measurements results for an open office. Measurements were taken along the passage in the building with most Line-of-sight between the access point and the client. Differences

between the prediction and measurements results were minimal and a good correlation was achieved until up to 22.5 meters. At 25 meters a line of sight was lost, the signal strength was affected which resulted in 6dB loss. The predicted and measured signal strength is –46.14dBm and –51.26dBm respectively. In general, the signal is very strong and could still achieve bit rate of 11Mb/s as shown in Table 01. Wi-Fi could be adopted for schools, community centers, medical centers and libraries for broadband access in the rural and under-served communities.

E. Radio Link Calculation for Outdoor Signal Level Predictions

To do outdoors coverage using wireless LAN, calculations of radio link budget and distances is very critical as they are many factors that can severely affect the quality of the signal. In free space, propagation model are used to predict received signal strength when the transmitter and receiver have a clear, unobstructed line-of-sight path between them. As the radio signal travels the signal will be lost in free space and the amount of free space loss can be empirically calculated.In a high frequency radio communication, line of sight condition between the transmitter and receiver is critical. A Fresnel zone is an area that no obstacle exists between transmitter and receiver. In figure 10, the 1st, 2nd and 3rd

Fresnel zones are shown.

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Figure 10: Fresnel Zones for radio Communications

In normal situation, 80% is used as a clearance reference in which no obstacles are permitted.

F. System Operating Margin (SOM)

The system Operating Margin can be calculated using equation: 1 listed below. SOM is the difference between the signal a radio is actually receiving versus what it needs for good data recovery that is the system receiver sensitivity

Free Space Loss = 20logF(MHz) + 20logD (in Miles). ……[1]

Where F is frequency in MHz and D is distance in miles. Again, the receiver signal level is given by equation: 2 below

Rx Signal Level = Tx Power – Tx Cable Loss + Tx Antenna Gain –FSL + Rx Antenna Gain - Rx Cable Loss. …[2]

To calculate System Operating Margin, we apply equation: 3

SOM = Rx Signal Level – Rx Sensitivity…………..[3]

Figure 11: Link Budget Calculation for Outdoors

In this case the operating frequency was 2400MHz with Tx Power of 20dBm, Tx Antenna Gain of 24dBi, Rx Antenna Gain of 24dBi, Tx and Rx cable losses of 2.4dB assuming a 3meters cable of 0.8dB/m is used and receiver sensitivity of –83 dBm. The type of antenna used is a Grid directional antenna with a maximum range of 25 kilometers for outdoor applications. The measurements were done for 25 kilometers starting from 0.5km and the Rx signal level is –30.9dBm, Free Space Loss is 94.1dB and Theoretical System Operating Margin of 52.1dB. The measurements were taken on a interval of 1 kilometer until 25 kilometers. At 25 kilometers, the Rx Signal Level is –64.8dBm, Free Space Loss is 128dB and Theoretical System Operating Margin is 18.2dB as is shown in figure 11 above.

A directional antenna with 24dBi gain for Access Point and Client point-to point communication, the operating margin for 25 kilometers distance is 18.2dB. This proved to be logical as using of a power amplifier to extend the distance was avoided to allow frequency reuse of the channels and escape from interference problems. The system operating margin is illustrated in figure 12 below

Figure 12: System Operating Margin

The graph of distance versus receiver signal level is shown in figure 13 below. The signal strength decreases as the distance increases. At a distance of 25 kilometers the receiver signal level is –64.8dBm, which is still enough for normal communication. On the same set of axes, the plot of distance versus Free Space Loss and distance versus Theoretical System Operating Margin is shown. At 0.5 kilometers we obtained FSL of 94.1dB and TSOM of 52.1dB.

The Effective Isotropic Radiated Power of the system can be calculated from the equation

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EIRP (dBm) = Tx Power – Tx Cable Loss + Tx Antenna Gain…………………………………………………[4]

From this equation the EIRP is 41.6dBm, which is still within the range of effective communication. This can be applicable in rural and under-served areas for universal access.

Figure 13: Simulation Results from WLAN design software

IV. Conclusion

More than half the world’s population live in rural and under-served areas. Rural communities promise essential new markets for contents access. The deployment of Wi-Fi for rural and under-served areas will be a major achievement for both the industry and the communities as a whole. Furthermore, if the WLAN deployment can further be interfaced with the existing BTS (Base Transceiver Stations) infrastructure, the common problems of cable theft for telecommunications operators could also be ironed out to a large extend.

V. References

[1] Peter Cukor and Lee W. McKnight“Knowledge Networks, The Internet and Development” itc.mit.edu/itel/docs/jun00/cukor_mck_tprc.pdf

[2]. Michael L. Best and Colin M. Maclay “Community Internet Access in

Rural Areas: Solving Economic

Sustainability Puzzle” Chapter 8

[3] Michael L. Best, Program inInternet & Telecom Convergence, Massachusetts Institute of Technology “Trends in Telecommunications Reform 2003”Chapter 7 pp 01

[5] David Cavin “Wireless LANs Mobile Ad hoc Networks”, pp19.

[4], [6-7] Alex (Sandy) Pentland, Richard Fletcher, Amir A. Hasson, MIT Media Laboratory “A Road to Universal Broadband Connectivity”, pp 2

[8] icommons.harvard.edu/userdocs/core_site/ioups_files/laporte_pres_wan.ppt

[9] ‘Access Point Capacity’ http://www.intel.com/business/bss/infrastructure/wireless/deployment/considerations.

[10] “Link Budget Calculation’ www.antennspecialisten.se.

[11]. http://www.ydi.com/calculation/som.php

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