Bandwidth Utilization: Multiplexing and Spreading

Bandwidh utilisasi adalah penggunaan bandwidth yang tersedia secara bijak untuk mencapai tujuan yang spesifik.

Penggunaan bandwidth secara efektif yang mana merupakan hal yang terbatas merupakan sebuah tantangan tersendiri dalam bidang teknologi komunikasi.

Terdapat 2 kategori untuk utilisasi bandwidth yaitu: multiplexing dan spreading.

Efisiensi dapat di capai dengan multiplexing, sedangkan privacy dan antijamming dapat dicapai dengan spreading.


Kapan saja ketika sebuah bandwidth pada sebuah media yang menghubungkan 2 device lebih besar daripada bandwidth yang dibutuhkan device tersebut, maka media link tersebut dapat dibagi.

Multiplexing adalah sekumpulan teknik yang memungkinkan transmisi simultan dari multiple(banyak) sinyal melewati sebuah data link.

Ketika data dan telekomunikasi meningkat, demikian juga traffic. Kita dapat mengakomodasikan peningkatan ini dengan menambah link individu secara terus-menerus setiap kali sebuah channel baru diperlukan, atau kita bisa menambah link dengan bandwidth yang lebih besar dan menggunakannya untuk membawa multile signal.

Media teknologi saat ini yang memiliki bandwidth yang besar seperti fiber optik dan microwaves, masingmasing memiliki bandwidth yang jauh melebihi kebutuhan rata-rata signal transmisi. Bila bandwidth yang digunakan melalui link tersebut lebih kecil dari bandwidth maksimal, maka sebenarnya besar maksimum bandwidth tersebut menjadi sia-sia.

Dalam sistem ter-multiplex, n line berbagi bandwidth dari sebuah link.


Pada diagram diatas, line di kiri secara langsung mengtransmisikan ke multiplexer (MUX), yang mana mengkombinasikannya dalam sebuah stream.

Pada sisi penerima, stream tersebut masuk ke demultplexer (DEMUX), yang mana memisahkan aliran tersebut kembali ke komponen transmisinya dan menyalurkannya kembali ke linenya sendiri.

Dalam diagram di atas, link merujuk ke path fisik dan chanel merujuk ke bagian dari link yang membawa transmisi antara pasangan line. Sebuah link dapat memiliki banyak channel.

Terdapat 3 teknik dasar multiplexing:  frequency-division multiplexing(analog), wavelength-division multiplexing(analog), dan time-division multiplexing(analog).

Frequency-Division Multiplexing
Frequency-division multiplexing (FDM)  adalah teknik analog yang dapat diaplikasikan ketika bandwidth pada sebuah link lebih besar daripada kombinasi bandwidth dari signal yang akan ditransmisikan. Pada FOM, signal yang dihasilkan dari setiap device pengirim memodulasi frekuensi carrier yang berbeda. Signal-signal termodulasi ini kemudian dikombinasikan kedalam komposit tunggal yang dapat di kirimkan melalui link. Frekuesni carrier dipisahkan oleh bandwidth yang cukup untuk mengakmodasi signal yang termodulasi. Range bandwidth ini adalah channel dimana bermacam-macam signal lewat. Channel dapat dipisahkan oleh strip band bandwidth pemisah yang tidak digunakan untuk mencegah signal dari overlapping. Sebagai tambahan, frekuensi carrier harus tidak boleh mengganggu frekuensi data yang original.


Spread Spectrum

Dalam spread spectrum, kita mengkombinasikan signal dari sumber yang berbeda untuk muat dalam bandwidth yang lebih besar, tetapi tujuan kita adalah mencegah penyadapan dan jamming. Untuk mencapai tujuan ini, teknik spread spectrum menambahkan redudancy.

Mobile Ad Hoc Networks (MANETs)

A mobile ad hoc network (MANET) is a continuously self-configuring, self-organizing, infrastructure-less network of mobile devices connected without wires. It is sometimes known as “on-the-fly” networks or “spontaneous networks”.

Vehicular ad hoc networks (VANETs)
VANETs are used for communication between vehicles and roadside equipment. Intelligent vehicular ad hoc networks (InVANETs) are a kind of artificial intelligence that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents. Vehicles are using radio waves to communicate with each other, creating communication networks instantly on-the-fly while vehicles are moving on the roads.

Smart phone ad hoc networks (SPANs)
A SPAN leverages existing hardware (primarily Wi-Fi and Bluetooth) and software (protocols) in commercially available smartphones to create peer-to-peer networks without relying on cellular carrier networks, wireless access points, or traditional network infrastructure. Most recently, Apple’s iPhone with version 7.0 iOS and higher have been enabled with multi-peer ad hoc mesh networking capability, in iPhones, allowing millions of smart phones to create ad hoc networks without relying on cellular communications. It has been claimed that this is going to “change the world”.

Wireless mesh networks
Mesh networks have its name taken from the topology of the resultant network. In a fully connected mesh, each node is connected to every other node, forming a “mesh”. A partial mesh, therefore, has a topology where some nodes are not connected to others, although this term is seldom in use. Wireless ad hoc networks can take the form of a mesh networks or others. A wireless ad hoc network does not have fixed topology, and its connectivity among nodes is totally dependent on the behavior of the devices, their mobility patterns, distance with each other, etc. Hence, wireless mesh networks are a descendent of wireless ad hoc networks, with special emphasis on the resultant network topology. Also, most wireless mesh networks have relatively slow or infrequent mobility, and hence link breaks seldom happen. Google Home, Google Wi-Fi, and Google OnHub all support Wi-Fi mesh (i.e., Wi-Fi ad hoc) networking. Apple’s Airport allows the formation of wireless mesh networks at home, connecting various Wi-Fi devices together and providing good wireless coverage and connectivity at home.

Army tactical MANETs
Army has been in need of “on-the-move” communications for a long time. Ad hoc mobile communications come in well to fulfill this need, especially its infrastructureless nature, fast deployment and operation. Military MANETs are used by military units with emphasis on rapid deployment, infrastructureless, all-wireless networks (no fixed radio towers), robustness (link breaks are no problem), security, range, and instant operation. MANETs can be used in army “hopping” mines, in platoons where soldiers communicate in foreign terrains, giving them superiority in the battlefield. Tactical MANETs can be formed automatically during the mission and the network “disappears” when the mission is over or commissioned. It is sometimes called “on-the-fly” wireless tactical network.

Air Force UAV Ad hoc networks
Unmanned aerial vehicle, is an aircraft with no pilot on board. UAVs can be remotely controlled (i.e., flown by a pilot at a ground control station) or can fly autonomously based on pre-programmed flight plans. Civilian usage of UAV include modeling 3D terrains, package delivery (Amazon), etc. UAVs have also been used by US Air Force for data collection and situation sensing, without risking the pilot in a foreign unfriendly environment. With wireless ad hoc network technology embedded into the UAVs, multiple UAVs can communicate with each other and work as a team, collaboratively to complete a task and mission. If a UAV is destroyed by an enemy, its data can be quickly offloaded wirelessly to other neighboring UAVs. The UAV ad hoc communication network is also sometimes referred to UAV instant sky network.

Navy ad hoc networks
Navy ships traditionally use satellite communications and other maritime radios to communicate with each other or with ground station back on land. However, such communications are restricted by delays and limited bandwidth. Wireless ad hoc networks enable ship-area-networks to be formed while at sea, enabling high speed wireless communications among ship, enhancing their sharing of imaging and multimedia data, and better co-ordination in battlefield operations. Some defense companies (such as Rockwell Collins and Rohde & Schwartz) have produced products that enhance ship-to-ship and ship-to-shore communications.

Wireless sensor networks
Sensors are useful devices that collect information related to a specific parameter, such as noise, temperature, humidity, pressure, etc. Sensors are increasingly connected via wireless to allow large scale collection of sensor data. With a large sample of sensor data, analytics processing can be used to make sense out of these data. The connectivity of wireless sensor networks rely on the principles behind wireless ad hoc networks, since sensors can now be deploy without any fixed radio towers, and they can now form networks on-the-fly. “Smart Dust” was one of the early projects done at U C Berkeley, where tiny radios were used to interconnect smart dust. More recently, mobile wireless sensor networks (MWSNs) have also become an area of academic interest.

Ad hoc home smart lighting
ZigBee is a low power form of wireless ad hoc networks that is now finding their way in home automation. Its low power consumption, robustness and extended range inherent in mesh networking can deliver several advantages for smart lighting in homes and in offices. The control includes adjusting dimmable lights, color lights, and color or scene. The networks allow a set or subset of lights to be controlled over a smart phone or via a computer. The home automation market is tipped to exceed $16 billion by 2019.

Ad hoc street light networks
Wireless ad hoc smart street light networks are beginning to evolve. The concept is to use wireless control of city street lights for better energy efficiency, as part of a smart city architectural feature. Multiple street lights form a wireless ad hoc network. A single gateway device can control up to 500 street lights. Using the gateway device, one can turn individual lights ON, OFF or dim them, as well as find out which individual light is faulty and in need of maintenance.

Ad hoc networked of robots
Robots are mechanical systems that drive automation and perform chores that would seem difficult for man. Efforts have been made to co-ordinate and control a group of robots to undertake collaborative work to complete a task. Centralized control is often based on a “star” approach, where robots take turns to talk to the controller station. However, with wireless ad hoc networks, robots can form a communication network on-the-fly, i.e., robots can now “talk” to each other and collaborate in a distributed fashion. With a network of robots, the robots can communicate among themselves, share local
information, and distributively decide how to resolve a task in the most effective and efficient way.

Disaster rescue ad hoc network
Another civilian use of wireless ad hoc network is public safety. At times of disasters (floods, storms, earthquakes, fires, etc.), a quick and instant wireless communication network is necessary. Especially at times of earthquakes when radio towers had collapsed or were destroyed, wireless ad hoc networks can be formed independently. Firemen and rescue workers can use ad hoc networks to communicate and rescue those injured. Commercial radios with such capability are available on the market.

Hospital ad hoc network
Wireless ad hoc networks allow sensors, videos, instruments, and other devices to be deployed and interconnected wirelessly for clinic and hospital patient monitoring, doctor and nurses alert notification, and also making senses of such data quickly at fusion points, so that lives can be saved.


Quality of Services dalam Jaringan Telekomunikasi

Quality of Services adalah deskripsi dari pengukuran terhadap perfomansi pada sebuah layanan.

Contoh penerapan QoS dalam:

  • layanan jaringan telepon
  • layanan jaringan internet
  • layanan cloud computing

Secara khusus pengertian Qos ini adalah kinerja layanan yang diterima oleh user dalam jaringan.

Untuk megukur QoS secara kuantitatif, beberapa aspek terkait layanan jaringan yang biasa dijadikan pertimbangan adalah:

  • Packet loss
  • Bit rate
  • Throughput
  • Transmission delay
  • Ketersediaan layanan
  • Jitter

Dalam bidang Jaringan komputer dan jaringan telekomunikasi packet-switched lainnya, QoS lebih mengacu pada prioritasi traffic dan mekanisme kontrol reservasi sumber daya daripada pencapaian kualitas service.

QoS adalah kemampuan untuk memberikan prioritas berbeda pada aplikasi, pengguna, atau arus data yang berbeda-beda, atau untuk menjamin tingkat kinerja tertentu terhadap flow data.

QoS sangat penting untuk transport traffic yang memiliki kebutuhan khusus. Misalnya pengembangan teknologi Voice over IP untuk memungkinkan jaringan komputer digunakan seperti jaringan telepon untuk percakapan audio, serta mendukung aplikasi baru dengan kebutuhan kinerja jaringan yang lebih baik.