Question

1. a. What is a diversity antenna?

b. What is its purpose in a cell phone?

c. How will the phone's electrical performance be affected without it?

Answer 1

Ans a.

Antenna diversity is a technique that can be used to improve radio communication and maximize the chance of a packet getting through at a given time and in a given position between a receiver and transmitter in a non-static environment.

Antenna diversity, uses the concept of transmitting multiple copies of the “same” or slightly modified symbols through different antennas to improve the reliability of the signal. Simply saying, we get 2 or more “radio links” with the “same” information, thus when there is a big distortion (e.g. deep fade) on one link, the probability that the other is also bad is smaller.

The most common scheme for antenna/transmit diversity is to use Alamouti encoding for assuring the orthogonality between the transmission streams transmitted from the two (or more) antennas. Alamouti scheme is also used in LTE for the antenna diversity (also called SFBC - space frequency block coding).

Ans b.

Cell phones contain at least one radio antenna in order to transmit or receive radio signals. An antenna converts an electric signal to the radio wave (transmitter) and vice versa (receiver). Some cell phones use one antenna as the transmitter and receiver while others, such as the iPhone 5, have multiple transmitting or receiving antennas.

An antenna is a metallic element (such as copper) engineered to be a specific size and shape for transmitting and receiving specific frequencies of radio waves. A diversity antenna is used to maximize the chance of a packet getting through at a given time and in a given position between a receiver and transmitter. Mobile phone towers also often take advantage of diversity - each face (sector) of a tower will often have two antennas; one is transmitting and receiving, while the other is a receive only antenna. Two receivers are used to perform diversity reception. The use of multiple antennas at both transmit and receive results in a multiple-input multiple-output (MIMO) system. The use of diversity techniques at both ends of the link is termed space–time coding. While older generation cell phones have external or ex tractable antennas, modern cell phones contain more compact antennas inside the device thanks to advanced antenna technologies. It’s important to understand that any metallic components in the device can interact with the transmission antenna and contribute to the pattern of the transmitted signal.

Ans c.

If we use cell phones without antenna than it may lead to several problems, including static, poor reception, dropped calls, slow downloads, and low wireless signals.

The antenna is responsible for many of the cell phone’s functions including phone calls and Wi-Fi connection. When the antenna is damaged or not used, your cell phone will not function properly. The phone may:

• Not show a signal
• Fail to connect to Wi-Fi
• Not connect to data services
• Drop calls
• Download slowly