Blog: Data transfer between iOS and Android devices using Wi-Fi

Transferring photo and video files between mobile devices is one of the most common everyday tasks performed by smart phone users. In one of our recent projects we had a task to define and implement the most efficient way for data transfer between the two most popular platforms: iOS and Android.


The biggest challenge we faced when working on the project was that the file transfer speed was very slow (~0.16 Mbit/s) when using Bluetooth, which had to do with Bluetooth hardware specification. It was not as important for transferring 2 bytes of data, but for a 3-4 MB image file transfer, which took up to 3 minutes, it was quite critical. To solve this problem we’ve decided to switch to Wi-Fi, which has allowed us to transfer the file of the same size within just 2-3 seconds.

Bluetooth wireless connection operates within the ISM band,that is used for various appliances and wireless networks (the license-free ISM band spectrum is 2.4 – 2.4835 GHz). Wi-Fi is based on the IEEE 802.11 standard, and operates at 0.9; 2.4; 3.6; 5 GHz frequencies allowing for 54 Mbit/s data transfer speed.

As opposed to Bluetooth networks, Wi-Fi networks must have a wireless access point.

Wireless Access Point (WAP)
is a base station which provides wireless access to a wired or wireless network, or it can be used to set up a new wireless network.

Every 100ms WAP broadcasts its service set identifier (SSID) with the help of special signal packets at the rate of 0.1 Mbit/s. That is why 0.1 Mbit/s is the slowest data transfer speed for Wi-Fi. Knowing SSID, a client can find out if it is possible to connect to the specific WAP.


Wi-Fi Network Pros and Cons

1. The main advantage of a Wi-Fi network, compared to Bluetooth, is its data transfer speed. However just like in the case with Bluetooth, we were not able to reach the speed stated in the specification (54 Mbit/s for 802.11g standard). Nonetheless, we found a significant difference between Bluetooth and Wi-Fi data transfer rate.

2. Another Wi-Fi advantage would be the fact that it allows to connect different platforms: iOS and Android, for instance. When there is a need to support Windows phone, BlackBerry, Tizen- there shouldn’t be any problems.

As for Wi-Fi disadvantages, the most important ones are the need for a WAP for the network establishment and the dependency on its stable operation. While in big cities Wi-Fi access points are widespread, in the suburbs it may be difficult to find one, and there may be no access points in rural areas. Just to add to this, access points in public areas may be overloaded or may operate very slowly because of many connections. In theory an access point is supposed to serve 2048 simultaneous connections, in reality however we end up with only 24 connections.


Transition to Wi-Fi data transfer within Bluetooth network

As shown in the picture, Device 1 and Device 2 are positioned in both Bluetooth and Wi-Fi networks. The protocol developed by DB Best team identifies any device positioned in both Bluetooth and Wi-Fi networks as a single device, this way providing an immediate start of data transfer via Wi-Fi with no need to search and identify the receiving device in another network.

Thus, the scalability of the wireless data transfer protocol allows to overcome the problem with slow data transfer in a case of large data sets. At the same time the flexible architecture of the protocol’s carrying engine enables implementation of the new technologies for data transferring between mobile devices with different platforms (e.g. iOS and Android in this case). Just recently our team has successfully implemented a new Multipeer Connectivity module without having to modify the engine configurations.