Space Division Multiplexing : Diagram, Working, Advantages, Disadvantages & Its Applications

Multiplexing in telecommunication and computer networks is a type of technique used to combine & transmit numerous data signals throughout a single medium. In the multiplexing method, multiplexer (MUX) hardware plays a significant role in attaining multiplexing by merging ‘n’ input lines to generate a single output line. So this method follows mainly the many-to-one concept which means n-input lines and single output line. There are different types of multiplexing techniques like; FDM, TDM, CDM, SDM & OFDM. This article provides brief information on one of the types of multiplexing techniques like; space division multiplexing or SDM.

What is Space Division Multiplexing (SDM)?

A multiplexing technique within a wireless communication system is used to enhance the system capacity by simply exploiting the physical separation of users is known as space division multiplexing or spatial division multiplexing (SDM). In this multiplexing technique, several antennas are utilized at both the ends of the transmitter & receiver to make parallel communication channels. These communication channels are independent of each other, which allows several users to transmit data simultaneously within a similar frequency band except for interference.

The wireless communication system capacity can be improved by simply including more antennas to form more independent channels. This multiplexing technique is used commonly within wireless communication systems like; Wi-Fi, satellite communication systems & cellular networks.

SDM in Submarine Optical Cable Example

Space division multiplexing in the submarine optical cable application is divided into three transmission systems; single-core fiber C-band, single-core fiber C+L-band & multi-core fiber C-band transmission. The three transmission system light path diagram is shown below.

A single-core fiber C-band in a submarine optical cable transmission system is equipped only with EDFA equipment for improving the signal. EDFA (Erbium Doped Fiber Amplifier) is one kind of OFA that is an optical amplifier through erbium ions included in the optical fiber core. EDFA has some features like; low noise, high gain & polarization independent. It amplifies optical signals within the 1.55 μm (or) 1.58 μm band.

The single-core C+L-band transmission system requires two EDFAs to improve the two band signals correspondingly. The multi-core fiber C-band transmission system is very complicated and it requires fanning out every fiber core & inputting it to the signal amplifier, and after that fan in the amplifier signal into the multi-core fiber cable.

Whenever the signal-to-noise ratio of the 3-channel transmission system is about 9.5dB, then the single-core fiber C+L-band transmission system needs 37 optical fiber pairs to attain the maximum optical cable capability transmission.

Multicore fiber C-band transmission system needs 19 to 20 pairs of fibers to attain the highest transmission ability. Single-core fiber C+L-band transmission system requires only thirteen fiber cable pairs to spread the highest capacity; however, its highest capacity is 70% of the single-core C-band fiber transmission only.

In SDM technology, the distance of every submarine optical cable is set to 60km to calculate the required voltages by the three transmission systems. Single-core C-band & C+L-band need lower voltages through 15 kV of maximum voltage. As compared to multi-line FOC transmission systems, their voltages are lesser because multi-core fiber transmission systems need extra amplifiers for completing the transmission.

In three transmission systems of space division multiplexing, the transmission ability of single-core fiber C+L-band & multi-core C-band is slighter as compared to single-core fiber C-band transmission. Single-core fiber C-band & C+L-wave systems can utilize lower voltages & power utilization as compared to multi-core systems if a similar capacity is attainable through multi-core.

Space Division Multiplexing Working

Space Division Multiplexing (SDM) works by exploiting the spatial dimension to transmit multiple independent data streams simultaneously. Here’s a simplified explanation of how it works:

• Spatial Separation: SDM relies on physically separating the transmission paths for different data streams. This separation can be achieved using various techniques depending on the medium of transmission, such as using different optical fibers, antenna elements, or acoustic paths.
• Multiple Channels: Each spatially separated path represents a distinct communication channel. These channels can be utilized to transmit independent data streams concurrently without interfering with each other.
• Data Encoding and Modulation: Before transmission, the data intended for each channel undergoes encoding and modulation techniques to convert it into a format suitable for transmission over the chosen medium. This typically involves converting digital data into analog signals modulated at specific frequencies or other properties suitable for the transmission medium.
• Simultaneous Transmission: Once the data is encoded and modulated, it is transmitted simultaneously over the spatially separated channels. This simultaneous transmission allows for increased data throughput and efficient utilization of the available communication resources.
• Receiver Decoding: At the receiving end, the signals from all the spatial channels are received and processed separately. Each channel is demodulated and decoded to recover the original data streams. Since the channels are spatially separated, there is minimal interference between them, allowing for reliable data recovery.
• Integration of Data Streams: Finally, the recovered data streams from all the channels are integrated to reconstruct the original transmitted data. This integration process depends on the specific application and may involve tasks such as error correction, synchronization, and data aggregation.

Overall, space division multiplexing enables the simultaneous transmission of multiple independent data streams by leveraging spatial separation, thereby increasing communication capacity and efficiency. It is commonly used in various communication systems, including optical fiber networks, wireless communication, satellite communication, and underwater acoustic communication.

Space Division Multiplexing Examples

The first example of SDM is cellular communication because in this communication the equal set of carrier frequencies are used again within cells that are not close to each other.

• Optical Fiber Communication: In fiber optic communication systems, multiple channels can be transmitted simultaneously through the same fiber by using different spatial paths. Each spatial path can represent a different wavelength (Wavelength Division Multiplexing – WDM) or a different polarization state (Polarization Division Multiplexing – PDM). This allows for increased data transmission capacity without having to lay down additional physical fiber cables.
• Multiple Antenna Systems: In wireless communication, multiple-input multiple-output (MIMO) systems utilize multiple antennas at both the transmitter and receiver to improve spectral efficiency. Each antenna pair forms a spatial channel, and data is transmitted over these channels simultaneously, effectively increasing the capacity of the wireless link.
• Satellite Communication: Satellite communication systems often employ SDM techniques to transmit multiple signals simultaneously using different frequency bands or spatial paths. This allows for more efficient utilization of satellite resources and increased data throughput for applications such as broadcasting, internet services, and remote sensing.
• Underwater Acoustic Communication: In underwater environments, acoustic waves are used for communication due to their ability to travel long distances. SDM can be employed by using multiple hydrophones and transmitters to create spatially separated channels, allowing for simultaneous transmission of multiple data streams and increasing the overall communication capacity.
• Integrated Circuit Interconnects: Within electronic devices, such as computer processors or networking equipment, space division multiplexing techniques can be applied to interconnect multiple components or cores on a chip. By routing signals through different physical paths, data can be transmitted concurrently between various processing units, enhancing overall system performance and throughput.

Advantages & Disadvantages

The advantages of space division multiplexing include the following.

• An SDM technique improves optical fiber’s spatial density in unit cross-section.
• It boosts the number of spatial transmission channels within a common cladding.
• The SDM is a combination of FDM or frequency division multiplexing & TDM or time division multiplexing.
• It transmits messages with the utilization of a specific frequency, so a particular channel can be utilized against a particular frequency band for some time.
• This multiplexing technique simply allows an optical fiber to transmit several signals that are sent at various wavelengths exclusive of interfering with each other.
• SDM develops energy efficiency & significantly allows lower costs for each bit.
• SDM technique improves the spectral efficiency for each fiber by simply multiplexing the signals within orthogonal LP modes in FMF (few-mode fibers) & multi-core fibers.
• The development is fairly simple & no fundamental new optical components are necessary.
• Best use of Bandwidth.
• Fixed frequency can be used again within SDM.
• SDM can be implemented within pure optical cables.
• Its throughput is extremely high because of the optical cables.
• Best use of frequency because of several multiplexing techniques & fiber optic.

The disadvantages of space division multiplexing include the following.

• The cost of SDM is still increasing significantly because of improving the number of transmission channels.
• Multiplexing uses complex algorithms & protocols to merge and divide the various signals being broadcasted. So this improves the difficulty of the network & makes it more hard to maintain & troubleshoot.
• Multiplexing causes interference between the signals being broadcasted, which can corrupt the value of the transmitted data.
• This multiplexing technique needs a certain quantity of bandwidth for the multiplexing procedure, which can decrease the amount of bandwidth available for real data transmission.
• Implementing & maintaining this multiplexing is expensive because of the complexity & required specialized equipment.
• This multiplexing makes it more difficult to save the transmitted data because several signals are being sent above a similar channel.
• In SDM, an inference may occur.
• SDM faces high inference losses.
• In SDM, the same set of frequencies or the same set of TDM signals are used in two different places

Space Division Multiplexing Applications

The applications of space division multiplexing include the following.

• Space division multiplexing is used in terrestrial networks through two different methods; SDM-compatible components arranged within both transmission & switching infrastructures (or) SDM implementation only within the switching architecture.
• Space-division multiplexing technique within MIMO wireless communication and fiber-optic communication is used to broadcast independent channels that are separated within space.
• SDM is used in cellular networks in the Multiple Input Multiple Output technology form, which uses several antennas at both the ends of the transmitter & receiver to enhance the value as well as capability of the communication link.
• SDM refers to a method to understand optical fiber multiplexing with space division.
• SDM technique is used for optical data transmission wherever multiple spatial channels are used like in multi-core fibers.
• The spatial division multiplexing technique for optical fiber transmission helps overcome the capability limit of WDM.
• SDM is used in GSM technology.

Thus, this is an overview of space division multiplexing, working, examples, advantages, disadvantages, and applications. SDM technology conforms to the growth trend of OFC or optical fiber communication. This multiplexing technique is a major innovation & developed way of OFC technology. Here is a question for you, what is time division multiplexing or TDM?