Wi Fi
Wi-Fi
technology, based on the IEEE 802.11 standard, was developed as a
wireless replacement for the popular wired IEEE 802.3 Ethernet standard. As
such, it was created from day one for Internet connectivity. Although Wi-Fi
technology primarily defines the link layer of a local network, it is so
natively integrated with the TCP/IP stack, that when people say they are using
Wi-Fi they implicitly mean that they are also using a TCP/IP for Internet
connectivity.
Riding on
the huge success of smart phones and tablets, Wi-Fi has become so ubiquitous
that people often refer to it as just “wireless.” Wi-Fi APs are deployed today
in most homes, as well as in almost all offices, schools, airports, coffee
shops and retail stores. The huge success of Wi-Fi is largely due to the
remarkable interoperability programs run by the Wi-Fi Alliance and to the
increasing demand in the market for easy and cost-effective Internet access.
Wi-Fi is integrated already into all new laptops, tablets, smartphones and TVs.
Taking advantage of the existing vast deployed infrastructure in homes and
enterprise, Wi-Fi’s natural next step is to connect the new age of things to
the Internet.
Wi-Fi
networks have a star topology, with the AP being the Internet gateway. The
output power of Wi-Fi is high enough to allow full in-home coverage in most
cases. In enterprise and in large buildings, more than one AP is often deployed
in different locations inside the building to increase the network coverage. In
large concrete buildings dead spots may be found due to multipath conditions.
To overcome dead signal receptions spots in some cases, various Wi-Fi products
include two antennas for diversity.
Most Wi-Fi
networks operate in the ISM 2.4-GHz band. Wi-Fi can also operate in the 5-GHz
band where more channels exist and higher data rates are available. However,
since the range of 5-GHz radios inside buildings is shorter compared to 2.4
GHz, 5 GHz is mainly used in enterprise applications along with multiple APs to
ensure good Wi-Fi coverage.
Wi-Fi and
TCP/IP software are fairly large and complex. For laptops and smartphones with
powerful microprocessors (MPUs) and large amounts of memory, this imposes no
issue. Until recently, adding Wi-Fi connectivity to devices with little
processing power such as thermostats and home appliances was not possible or not
cost effective. Today, silicon devices and modules coming out on the market
embed the Wi-Fi software and the TCP/IP software inside the device. These new
devices eliminate most of the overhead from the MPU and enable wireless
Internet connectivity with the smallest microcontroller (MCU). The increasing
level of integration in these Wi-Fi devices also eliminates all required radio
design experience and reduces the barriers of Wi-Fi integration. To enable high
data rates (over 100MBps in some cases) and good indoor coverage, Wi-Fi radios
have fairly large power consumption.
For some
IoT devices, which run on batteries and cannot be charged frequently, Wi-Fi can
be too power hungry. Although the peak current of Wi-Fi radios cannot be
reduced by much, new silicon devices apply advanced sleep protocols and fast
on/off time to reduce the average power consumption dramatically. Since most
IoT products do not need the maximum data rates Wi-Fi offers, clever power
management design can efficiently draw bursts of current from the battery for
very short intervals and keep products connected to the Internet for over a
year using two AA alkaline batteries.
Today you
can buy a Wi-Fi based sports watch that uploads workout data to the Internet.
Most Wi-Fi APs claim support for up to 250 simultaneously connected devices.
Enterprise-grade APs can support even larger number of connections, and some
popular consumer APs handle no more than 50. To summarize,
Wi-Fi is
the most ubiquitous wireless Internet connectivity technology today. Its high
power and complexity has been a major barrier for IoT developers, but new
silicon devices and modules reduce many of the barriers and enable Wi-Fi
integration into emerging IoT applications and battery-operated devices. WiFi
specification
1.1.1
Wifi Topologies
Access
point
Sensor nodes may connect to any standard WiFi router which is configured as Access Point (AP) and then send the data to other devices in the same network such as laptops and smartphones. This is the common case when implementing home sensor networks and when using the data inside an Intranet. Once associated with the Access Point, the nodes may ask for an IP address by using the DHCP protocol or use a preconfigured static IP. The AP connection can be encrypted, in this case, you have to specify also the pass-phrase or key to the WiFi module. The WiFi module supports these security modes: WEP-128, WPA2-PSK , WPA1-PSK, and WPA-PSK mixed mode.
Nodes may also connect to a standard WiFi router with DSL or cable connectivity and send the data to a web server located on the Internet. Then users are able to get this data from the Cloud. This is the typical scenario for companies which want to give data accessibility services.
Ad-hoc mode
with iPhone/Android
The
following diagram shows how Android and iPhone devices can communicate directly
with the WiFi through an Adhoc WiFi network without any extra router or
gateway.
Advantages
that are already inherent in Wi-Fi: