What is the difference between Bluetooth 2.0 and 4.0 in android?

The main difference is that Bluetooth 2.0 is not as fast as Bluetooth 4.0. Below is a description of each version of Bluetooth. \x0d\\\x0d\\1.1 is the earliest version of Bluetooth, with a transmission rate of 748~810kb/s. Because of its early design, it is susceptible to interference by products of the same frequency, affecting the quality of communication. \x0d\ Bluetooth 1.2 standard \x0d\1.2 is also only 748~810kb/s transmission rate, but with the addition of (improve Software) anti-jamming frequency hopping function. \x0d\\ Bluetooth 2.0 standard \x0d\2.0 is an improved version of 1.2, the transmission rate is about 1.8M/s~2.1M/s, it starts to support duplex mode - that is to say, one side of the voice communication, and at the same time, can also be transferred to the file/high-quality picture, of course, the 2.0 version also supports the Stereo operation. \x0d\\ The most widely used standard is Bluetooth 2.0+EDR, which was launched in 2004, and products supporting Bluetooth 2.0+EDR appeared in large numbers in 2006. \x0d\ Although the Bluetooth 2.0+EDR standard has made a lot of technical improvements, the complexity of the configuration process and the high power consumption of the device, which has been carried over from the 1.X standard, still exists. \x0d\ Bluetooth 2.1 standard \x0d\ August 2, 2007, the Bluetooth technology alliance today officially approved the Bluetooth version 2.1 specification, that is, "Bluetooth 2.1 + EDR", can be freely used by future devices. And 2.0 version of the same generation of products, is still occupying a larger share of the Bluetooth market, relative to the 2.0 version is mainly to improve the standby time of more than 2 times, there is no fundamental change in the technical standards. \x0d\ Bluetooth 3.0 standard \x0d\ April 21, 2009, Bluetooth Technology Alliance (Bluetooth SIG) officially promulgated a new generation of standard specifications "Bluetooth Core Specification Version 3.0 High Speed" (Bluetooth Core Specification Version 3.0), Bluetooth 3.0 is the core of the " The core of Bluetooth 3.0 is "Generic Alternate MAC/PHY" (AMP), a new alternate RF technology that allows the Bluetooth protocol stack to dynamically select the correct RF for any task. \x0d\ Bluetooth 3.0 increases the data transfer rate to approximately 24Mbps (i.e., 802.11 WI-FI can be invoked for high-speed data transfer when needed). In terms of transmission speed, Bluetooth 3.0 is eight times faster than Bluetooth 2.0, and can be easily used for data transfer between VCR to HDTV, PC to PMP, and UMPC to printer, but both parties need to meet this standard to realize the function. \x0d\ Bluetooth 4.0 standard \x0d\ Bluetooth 4.0 specification was officially released on July 7, 2010, the new version of the biggest significance of low power consumption, while enhancing the compatibility of devices between different OEMs, and reduce the latency, the theoretical maximum transmission speed is still 24Mbps (i.e., 3MB/s), the effective range of coverage is expanded to 100 meters (the previous version is 10 meters) . The standard chip is used by a large number of cell phones and tablet PCs, such as Apple The New iPad tablet PC, and Apple iPhone 5, Meizu MX4, HTC One X and other cell phones with Bluetooth 4.0. \x0d\ Bluetooth 4.1 standard \x0d\ Bluetooth 4.1 was released on December 6, 2013, and LTE radio signals between if the simultaneous transmission of data, then the Bluetooth 4.1 can be automatically coordinated between the two transmissions, theoretically reducing the other signals on the Bluetooth 4.1 interference. Improvements include faster and smarter connections, such as reduced reconnection times between devices, meaning that if a user goes out of range of Bluetooth 4.1 and is disconnected for a short period of time, the device will automatically connect when the user is back in range again, with a shorter response time than Bluetooth 4.0. The last improvement is to increase the efficiency of transmission, if the user is connected to a large number of devices, such as multiple wearable devices, the information between each other can be instantly sent to the receiving device. \x0d\\ In addition to this, Bluetooth 4.1 also adds more flexibility for developers, a change that does not have a great impact on the average user, but is important for software developers, because in order to cope with the gradual rise of wearable devices, Bluetooth must be able to support the connection of multiple devices at the same time. \x0d\ Currently there are relatively few cell phones that support this standard, and the Samsung GALAXY Note4 is one of the representative ones. \x0d\\ Bluetooth 4.2 standard \x0d\ On December 4, 2014, the latest Bluetooth 4.2 standard was issued, improving data transfer speeds and the degree of privacy protection, and access to the device will be able to directly access the Internet via IPv6 and 6LoWPAN. Under the new standard Bluetooth signals want to connect or track the user's device must be authorized by the user, otherwise Bluetooth signals will not be able to connect and track the user's device. \x0d\ speed-wise it has become even faster, with data transfer speeds between two Bluetooth devices increasing by 2.5 times as the capacity of Bluetooth Smart (Bluetooth Smart) packets is increased to hold the equivalent of about 10 times the previous amount of data. The Bluetooth version is naturally the more advanced the better, taking into account the transmission distance and power consumption, the latest Bluetooth 4.1 is preferred, but there are not many Bluetooth 4.1 products on the market at the moment, while the mainstream Bluetooth 4.0 products are more cost-effective, and as for the Bluetooth 3.0, 2.1 and the following versions have lost the value of the purchase.