Question

(a) List the different types of DSL technologies. Explain Discrete Multitone Technique (DMT) (2 + 6 = 8) 7: with respect to ADSL (b) Write a brief note on architecture of a cellular network.

Answer 1

a)

DSL means Digital Subscriber Line. It is high-speed internet service for houses and businesses. Maximum all types of DSL services are asymmetric. All these services are divided as either asymmetric or symmetric. Services what are best for you is depends upon required support for simultaneous voice and video communications.

Asymmetric types of DSL connections gives more signal bandwidth for downloading from the internet service provider to the subscriber's computer than for uploading in another direction. Few forms of asymmetric DSL connections are ADSL(Asymmetrical Digital Subscriber Line) and VDSL(Very High Bit-Rate Digital Subscriber Line)

Symmetric DSL connection provides equal bandwidth for both downloads and uploads. It is very popular for business purpose. Few forms of symmetric DSL connections are SDSL(`Symmetric Digital Subscriber Line) and HSDL(High Bit-Rate Digital Subscriber Line)

Main thing of DMT is to divide the available bandwidth into huge number of connections. It can allocate the data so throughput of every sub channel is maximized. If it fails to carry any of the data, it will turn off and use of available bandwidth is optimized. ADSL DMT systems the downstream channels are divided into 256 4-kHz wide tones. The upstream channels are divided into 32 sub channels and standardized ADSL DMT parameter values are differ for both ATU-C and ATU-R.

b)

Changes in demand and less quality of existing service led mobile service providers to research ways to improve the quality of service and to support more users in their systems. Because the amount of frequency spectrum available for mobile cellular use was very limited, efficient use of the required frequencies was needed for mobile cellular coverage. In modern cellular telephonic system, rural and urban regions are divided into areas regarding to particular guidelines. Few necessary parameters, those are cell division and cell sizes, are determined by engineers experienced in cellular network system architecture.

Provisioning for each area is planned according to an engineering plan that contains

1. cells
2. clusters
3. Frequency reuse.

Cells: A cell is the basic geographic unit of a cellular system. The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending on the landscape. Because of constraints imposed by natural terrain and man made structures, the true shape of cells is not a perfect hexagon.

Cluster: A cluster is combination of number of cells. channels are not reused within a cluster

Frequency reuse: It is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from consecutive cells. The coverage area of cells is called as footprint. This footprint is very limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies never interfere.