a) Definition
Radio is a technology that allows the transmission of signals by modulation of electromagnetic wave with frequencies below those of light.
Radio waves are a form of electromagnetic radiation, and are created whenever a charged object accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum.
This is the range from a few tens of hertz to a few gigahertzes. Electromagnetic radiation travels (propagates) by means of oscillating electric and magnetic fields that pass through the air and the vacuum of space equally well, and does not require a medium of transport.
By contrast, other types of electromagnetic radiation, with frequencies above the RF range are gamma rays, X-rays and infrared, ultraviolet and visible light.
When radio waves pass a wire, their oscillating electric or magnetic field (depending on the shape of the wire) induces an alternating current and voltage in the wire. This can be transformed into audio or other signals that carry information. Although the word 'radio' is used to describe this phenomenon, the transmissions that we know as television, radio, radar and cell phone are all in the class of radio frequency emissions.
Radio takes many forms, including wireless network, mobile of all types, as well as radio broadcasting.
Radio communications means also wireless communication and is expected to be a key technology for the home automation market, as the use of RF-signals is highly desirable or necessary due to the ability to penetrate walls and ceilings.
With increasingly mobile lives, the desire to be connected anywhere and the demand for convenience on every level, consumers are rapidly adapting to wireless devices for a variety of personal and professional needs.
The new wireless revolution, using short-range radio frequency (RF) communication to do away with wires in homes and offices, is creating an unprecedented demand for cost-effective RF-ICs providing maximum integration, universal applicability, low power and flexibility.
b) Classification
Today the consumer two-way RF communications can be split into four categories:
- Mobile telephony (2G, 2.5G and 3G). These are the most complex and costly systems. Typically they also require the highest power consumption because of the need for high computing power and stringent requirements on transmitted signal spectrum and the sensitivity and selectivity of the receiver.
High data rate WLAN (Wireless Local Area Network) and WPAN (Wireless Personal Area Network). These standards have main focus on achieving very high data rates for short-range communication. Achieving low power consumption is secondary
3. Bluetooth (i.e. WPAN with medium data rate). This technology is optimised for short-range cable replacement. The most typical application example is communication between a mobile phone (or PDA) and a laptop. For many handheld Bluetooth applications low power consumption is very important.
4. Telemetry. These systems typically require a data rate of only a few kbps, as typical functionality is simple control and monitoring functions. The communication distance is in the range of a few meters up to hundred meters. Typical applications are home automation, remote keyless entry, automatic meter reading and alarm and security systems, electronic toys and game pads and audio and voice applications.
Figure 1 shows a very simplified picture of the different RF communication applications, and how they can be categorized according to cost, complexity, power consumption and data rate.
Figure 1. Description of cost, complexity and power consumption of two way wireless applications versus data rate
The telemetry systems, and more specifically home automation are expected to be a very important and fast growing field within this wireless application segment. These telemetry systems have common requirements for some of their most important features.
For example, many of products are battery operated and low current consumption is therefore essential to achieve maximum battery life. Very often products are physically small and require highly integrated single-chip solutions to minimize the size and to reduce the number of components required. In many cases a flexible solution that can be programmed for worldwide use is essential.
Wireless Home Automation Systems
The field of home automation is expanding rapidly as electronic technologies converge. The home network now encompasses communications, entertainment, security, convenience and information systems.
Typical applications within home automation are:
- Remote metering/control (Electricity, Gas, Water);
- Alarm/Security (Fire, Intruder, Social alarm);
- Power control (Power outlets, Light switches, Heating);
- Comfort functions (Blinds/shades/rollers, Curtains, Window control, Garage door openers, Building keyless entry);
- White goods (Freezer, Refrigerator, Oven/Microwave Oven).
Generally, there is no need for high data rates for these home automation applications as most functions are related to simple control and monitoring. Typical data rates are in the range of 1-40 kbps. However, what is especially important for home automation is the need for very low cost and very low power solutions.
In a few years a house can typically have a control and monitoring system with 50-200 intelligent radio nodes, used for e.g. remote lighting control, remote heating control (wireless thermostat) etc. With so many radios it is obviously very important to maximize the lifetime of the battery to keep maintenance cost down.
It is more and more recognized that Bluetooth is not the ideal solution for all short-range radio communication systems. Also, the required communication range (for a given transmitted output power) for a Home Automation system is generally longer compared to Bluetooth and WLAN. Finally, the cost targets of a complete Home Automation communication/system chip set is less than half of the cost of Bluetooth. This requires completely different system thinking and specification.
Moderate/low data rate wireless networks can not be used for all home network applications. E.g. data transfer between PCs, high-speed Internet access and steaming video applications would require WLAN or Bluetooth. However, having a central/gateway can enable very useful interactions of the various types of home networks.
E.g. for the low data rate control/monitoring networks it is desirable to have remote control of all these kinds of applications. In principle this can be done from anywhere in the world through any terminal (PC, mobile phone) which has Internet access. The home must be equipped with an Internet gateway.
This gateway could also have a central/master/bridge function for the various kinds of home networks installed. Then the mobile phone or PDA (or a combined device) can control the lights/heating by going through the central/gateway using e.g. Bluetooth communication.
Figure 2 shows how the various networks from figure 1 can co-exist and interact within a home. Each system is used for what it is optimised for, thus providing the overall optimum performance/cost ratio.
Figure 2. Home networking consist of various networks which co-exist and interconnect
In Europe the license exempt band centred at 433.92 MHz (about 1.7 MHz wide) is very important for general short range low power radio communication, and the more regulated 868-870 MHz band is also gaining popularity. It is an advantage that interference from Bluetooth and WLAN will be negligible.
The protocol used for the various home automation systems must be tailored for the specific application needs and the requirements on power consumption.
Figure 3. Components of a Wireless System
Information Source - any bit stream
Source Code r- reduction of bandwidth by means of compression voice, audio, video, etc
Middleware - transportation and communication setup
Channel Coder - adaptation to the wireless link