Learn about Simplex, Half Duplex and Full Duplex

There are 3 transmission modes, namely: Simplex (single duplex), half duplex (half duplex) and full duplex (full duplex). Transmission mode determines the direction of the signal flow between two connected devices.

The main difference between 3 transmission modes is that in single-mode transmission, the signal is transmitted in one direction. While in semi-duplex mode, the transmission can take place in both directions, but the two connected devices use channel rotation (ie the signal is only transmitted in one direction at a time. ).

On the other hand, in full-duplex mode, the signal transmission takes place in two directions simultaneously and the channel is used simultaneously by both connected devices.

Comparative Criteria Simplex Half Duplex Full Duplex Signal direction Unidirectional bidirectional, one direction in two directions, at the same time in two directions Send / Receive The sender can only send data The sender can send and receive data data, but only one action can be performed at a time The sender can send and receive data at the same time Performance Poor transmission mode Better than Simplex mode Best transmission mode Example Keyboard and monitor Telephone

Learn about Simplex, Half Duplex and Full Duplex Picture 1

Simplex

In the public transmission mode, communication between the sender and the receiver occurs in only one direction. The sender can only send data and the receiver can only receive data. The recipient cannot reply to the sender.

Single transmission is like a one-way street in which vehicles traveling in only one direction and no vehicles from the opposite direction are allowed to pass through.

Taking the relationship between the keyboard and the screen as an example, the keyboard can only send input to the screen and the screen can only receive input, and then display the content on it. The screen cannot respond or send any feedback to the keyboard.

Half Duplex

The communication between sender and receiver takes place in both directions in semi-duplex transmission, but only one direction at a time. The sender and the receiver can send and receive information, but only one party is allowed to send at a specific time. Half duplex is still like a one-way street, in which a vehicle traveling in the opposite direction must wait until the empty road can pass.

For example, in a walkie-talkie, both sides might speak, but it must be done one by one. 2 sides can not say at the same time.

Full duplex

In full-duplex mode, the communication between the sender and the receiver can take place simultaneously. The sender and receiver can transmit and receive signals at the same time. Full-duplex transmission mode is like a two-way street, in which vehicles can travel in both directions at the same time.

For example, in a telephone conversation, two people can communicate and both can freely talk and listen at the same time.

The main difference between 3 transmission modes

1. In simplex mode, the signal is sent in one direction. In semi-duplex mode, the signal is sent in both directions, but only one direction at a time. In full duplex mode, signals are sent in both directions at the same time.
2. In simplex mode, only one device can transmit a signal. In semi-duplex mode, both devices can transmit signals, but one device at a time. In full duplex mode, both devices can transmit signals at the same time.
3. Full duplex is better than semi-duplex and semi-duplex is better than single-duplex.
4. Single task: The keyboard sends commands to the screen. Screen cannot answer the keyboard.
5. Duplex sale: Using a walkie-talkie, both parties can communicate, but must take turns.
6. Full Duplex: Using the phone, both sides can communicate at the same time.
7. Full duplex transmission mode provides the best performance among the three methods, due to the fact that it maximizes the amount of available bandwidth.

The way the duplex affects the WiFi router

A WiFi router is a device that regulates, as well as plans, the flow of information to and from any electronic device that has WiFi (such as a laptop or smartphone) to the Internet, using a standard or interface. The specific protocol, called IEEE 802.11, operates in semi-duplex mode. WiFi is only a trademark for this specific IEEE standard (learn more about popular WiFi standards here).

WiFi devices connect wirelessly to the router by radio waves at 2.4 GHz or 5 GHz. The router plans, as well as ensuring that the correct flow of information between each connected device and the Internet is free of conflicts or loss with a Time Division Duplexing (TDD), which works like a full duplex.

TDD simulates full duplex by establishing or dividing the intervals between transmission and reception. Data packets flow in both directions based on time division. By splitting these time periods, devices connected in this way seem to be transmitted and received simultaneously.

Why can't the current router run in full-duplex mode?

The biggest problem in achieving full-duplex capability through radio waves is self-interference. This noise is stronger than the actual signal. Simply put, the noise in a full duplex system occurs when a single point is transmitting and receiving at the same time, it will also receive its own signal, thereby causing the phenomenon of self-interference.

Learn about Simplex, Half Duplex and Full Duplex Picture 2

In fact, full-duplex wireless transmission is something that can happen in the field of research and academia. This is largely achieved by eliminating self-interference at two levels. The first is by reversing the noise signal itself and then the noise reduction process is further enhanced digitally. A few students at Stanford University built full-duplex radio prototypes in 2010 and 2011. Some of these students went on to set up a commercial startup company called KUMU Networks, pledging will revolutionize the wireless network.

You can also find other works such as IBFD (In-Band Full-Duplex) of Cornell University and STAR (Simultaneous Transmit and Receive) of Photonic Systems Inc.

What about a wired LAN?

The wired part of the LAN communicates in full-duplex mode, with two twisted pairs of wires forming the Ethernet cable connection. Each pair is dedicated to transmitting and receiving packets simultaneously, so there is no data conflict or interference. This is everything you need to know about Ethernet cables.

Learn about Simplex, Half Duplex and Full Duplex Picture 3

Progress in WiFi connection

In IEEE 802.11 protocol, changes were made to reach better data range, throughput, or both. Since its formation between 1997 and 2013, WiFi standards have been revised from 802.11 to 802.11b / a, 802.11g, 802.11n and finally to 802.11ac. No matter how advanced they may be, they belong to the 802.11 family and will always run in half-duplex mode. Although improvements have been made, most notably including MIMO, running in half-duplex mode still halves the spectral efficiency.

Interestingly, routers supported by MIMO (multiple inputs and outputs) advertise their own data rates much faster. These routers use multiple antennas to transmit and receive multiple data streams at the same time, which can increase the overall transmission speed. This is usually found in 802.11n routers or newer models (presumably) with speeds of 600 megabits per second or more. However, because they operate in half-duplex mode, 50% (300 megabits per second) of the bandwidth is dedicated to transmission, while the remaining 50% is used for reception.

Full-duplex WiFi in the future

There is increasing commercial interest in full duplex wireless connectivity. The main reason is that advances in semi-duplex FDD and TDD are saturated. Software improvements, advancements in tuning and improving MIMO are becoming more and more difficult. As more devices connect wirelessly, the need to increase spectrum efficiency will eventually become paramount.

Full-duplex wireless connectivity has proven successful in instantaneously doubling this spectrum.

In areas with minimal impact on hardware, software reconfiguration, regulatory changes and monetary investment, the shift from full duplex to full duplex will begin to become increasingly prominent. than. Driven initially by the need for more capacity, you'll probably see full duplex WiFi in the near future, alongside the latest semi-duplex components.