Simple embedded wireless resolves rural public transport scheduling

by Mahesh Kiwalkar, Cypress Semiconductor , TechOnline India - October 09, 2008

Wireless protocol's frequency agility, data rate, and range offer a low-cost, robust system feeding a simple visual interface.

The problem
More than half the population in developing countries lives in the rural and suburban areas. Because car ownership is very low, the population relies heavily on the available public transportation system. Bus transport largely serves this demand of passenger transportation and thus plays a significant role in the overall rural economy. Several efforts have been made to improve this system but it is still largely plagued with low frequency, punctuality, and schedule inconsistency.

Because time translates to money in trade, relying on the accuracy of the bus transport schedule affects the daily income of many of the day laborers in these areas. This problem is further compounded as students depend on this sole mode of transport to attend classes at school.

The biggest issue is there is no set schedule in place for most of these routes. With many villages in remote areas, the closest destination could be 40 to 50 miles away. The unavailability of a schedule puts the load on the passenger to time his or her arrival at the bus stop empirically. When the passenger gets to the stop there is no way of telling whether the bus passed the stop or is yet to arrive.

Because this is a question of earning daily wages or missing school, it plays a critical part in daily life. Often times the next estimated bus arrival is few hours later or probably next day altogether. Vital information is whether the passenger missed the bus and if that was the last bus visit for the day for that particular route. The options are waiting for another bus, making the arduous walk to the destination, or returning home—all three of which are better than a fruitless wait at the bus stop.

What is needed
So let's look at what could possibly solve this issue. Key points needed in the solution would be:

  • Information transfer: A means of conveying critical information such as bus arrival, frequency of visit, etc. is needed.
  • Wireless: Because this solution applies to a moving vehicle, untethered communication is a necessity.
  • Interface: A simple visual interface which does not need the average commuter to be literate
  • Cheap but robust system: Economically viable and a system capable of sustaining rural infrastructure conditions such as power supply shortages, etc.
  • Maintenance and recurring cost: System which demands near zero maintenance and recurring cost

    Proposed solution
    The critical information mentioned above can be made available through simple, reliable, low cost embedded wireless, shown below.

    Essentially the solution is based on a hub and node architecture. A wireless hub consisting of a low cost wireless transceiver and a microcontroller are embedded in the bus stop infrastructure. The hub will typically sleep for most of the time. The interface to the average passenger is a simple set of green LEDs—the number of LEDs depending on the number of buses that visit that stop per day and their frequency of visit.

    The wireless node (transceiver-microcontroller) is embedded in each of the buses which visit the bus stop. Before the node transceiver modules are installed in the buses, they should be assigned non-identical IDs, which allows the hub firmware to differentiate between two nodes.

    Irrespective of the schedule they follow, when the bus arrives at the bus stop, the hub wakes up and queries the node for data. A two way handshake takes place to authenticate the node. The node then relays data information to the hub such as bus number, arrival time, and frequency of the visit for the day.

    The hub matches the data and switches on the corresponding LED to indicate the arrival of that particular bus and that particular trip of the day. The system firmware switches off all the LEDs at midnight for the next daily cycle. Having such a wireless embedded system will thus make the bus transportation system more comfortable and reliable for its rural passengers.

    Feasibility and viability
    Cost and power consumption are the two parameters of paramount importance for the feasibility of such a system in rural areas. Majority of the bus stops in rural areas do not have electrical power infrastructure readily available. Providing power to the bus stops exclusively for this system will not be a financially justifiable investment for the local government. Thus the wireless hub must run off batteries. To maximize the life of the hub system before having to change the batteries, the current draw of the system should be very small. Additionally the wireless technology employed should have the ability to sleep for a long time, because, between consecutive bus arrivals, the hub and nodes will be in a sleep mode. Keeping it simple, the solution can be a low data rate application and information packets can be just a few bytes. A simple point-to-point wireless technology is all that is needed. Range of about 10 meters is sufficient. A reliable hub-node communication protocol will drive the application. To minimize cost, bill of materials (BOM) should be minimal especially since there are no demanding firmware or memory requirements. Having a solution operating in the 2.4 GHz ISM band will allow its unrestricted worldwide implementation. Providing LEDs gives a simple visual interface and does not need the passenger to be literate. {pagebreak} Short range wireless technology space has been dominated by 2.4GHz technologies such as Wi-Fi, Bluetooth, Zigbee, and WirelessUSBTM [Ed. Note: Note to be confused with 3.1 to 10.6 GHz Certified Wireless USB.] Because the proposed solution is meant to be extremely simple so as to be feasible in rural environment, Wi-Fi and Bluetooth will be overkill in terms of cost and complexity. Data rate and range offered by WirelessUSB (250 kbps) are optimum for this particular application.

    A hardware-assisted interference avoidance protocol saves power.

    As shown above, an interference avoidance protocol monitors the interference strength of other RF signals using the radio's built-in received signal sensitivity indicator (RSSI) and a detection method of quality of service (QoS) to make decisions on channel hopping. This is a key performance differentiator when compared to Bluetooth because WirelessUSB 2.4GHz radios only hop to a different channel when it detects strong interference. This intelligent logic significantly reduces unnecessary power consumption compared to Bluetooth.

    In addition, Bluetooth radios typically cost twice that of an equivalent WirelessUSB radio and microcontroller (MCU). For example, the PRoC LP (programmable radio on chip) from Cypress Semiconductor provides a complete RF system solution with a single device and few discrete components. This integration helps greatly in cutting down the BOM and saves a good amount of printed circuit board space, too. The chip uses frequency-agile DSSS (direct-sequence spread spectrum) technology to mitigate interference. The in-system reprogrammable flash-based MCU enables firmware changes for future needs.

    Future outlook
    As proposed earlier a simple and low cost embedded wireless solution could thus help resolve schedule issues for rural public transport in developing nations. This could save time and money for commuters on a daily basis. Once this straightforward yet reliable solution is implemented in the public transport infrastructure, it will open up a multitude of possibilities for future advancements. For example since current consumption is small, power could be derived from solar panels installed on bus stops obviating the need for electricity or periodic battery change.

    Data collected from each bus can be logged and can help in route and schedule optimization. Based on the data collected for arrival times at each of the bus stops, bus routes and schedules could be modified to meet the demand accordingly. This solution could be further extended to school buses and taxicabs in suburban areas.

    In urban areas where infrastructure is not the impediment, the bus stops could be networked together and the logged data can be dispatched to a central base station. Using GIS (Geographic Information System) software at the base station, arrival times at subsequent bus stops could be mapped on the route. If this is made available to the public on the public transportation website, commuters could time their arrival to the specific bus stop.

    Rural and suburban public transport will thus benefit significantly from this low cost embedded wireless solution. It will increase credibility in the public transport system, encouraging more commuters to choose public transport over private transport, thus helping to resolve traffic congestion in urban areas.

    Mahesh Kiwalkar is the RF wireless staff applications engineer at Cypress Semiconductor. He has been involved with RF wireless design, development, and applications for more than six years. He received his Masters in Electrical Engineering from Pennsylvania State University. He can be reached at mahesh.kiwalkar@cypress.com.

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