Description

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

• Standard: Based on 802.11n (most common usage in homes today)
• Frequencies: 2.4GHz and 5GHz bands
• Range: Approximately 50m
• Data Rates: 600 Mbps maximum, but 150-200Mbps is more typical, depending on channel frequency used and number of antennas (latest 802.11-ac standard should offer 500Mbps to 1Gbps) 

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:

• IP-based communications – Wi-Fi is perfect for IoT – it’s already at home with IP addressing, including v6, and the broad family of IP protocols overall. And, very importantly, IoT always requires IP. If a given solution doesn’t natively speak IP then a separate gateway is required – adding expense, complexity, and potentially a single point of failure, all very bad ideas in any M2M application.
• Security and integrity – Wi-Fi already includes excellent security in the form of WPA2™, and Wi-Fi system vendors have been building highly-reliable, mission-critical, large-scale infrastructure solutions for years.
• Leveraging existing infrastructure – And that existing secure and reliable infrastructure can give M2M and IoT a head start in a vast number of venues where Wi-Fi is already hard at work. As they’re typically installed from scratch, and often for a single application, M2M or IoT solutions based on other technologies can get very, very expensive indeed. So, then: Wi-Fi-based IoT cost-effective? You bet!
• Flexibility – And it gets better – the under-development 802.11ah standard will likely re-claim access to the 900 MHz unlicensed band, and potentially other unlicensed spectrum below 1 GHz, for IoT. These lower frequencies are well-suited to IoT applications, where favorable propagation characteristics often matter but limited bandwidth does not.
• And beyond – As was noted above, most M2M and IoT applications won’t require long range or high throughput. But, if they do, or if applications evolve over time to require either or both of these factors, guess which wireless technology transparently scales to meet this need?