Wireless cellular network

G = Generation.

Basic principle (at beginning): re-use of frequencies.

Single hop widespread wireless connectivity to the wired world.

• Usually space divided into cells, and MTs assigned to a cell.

  • Communications: a voice call or a data session.

• Handoff/handover occurs when a MT moves to a new base station, while busy on a call.

• Highly supported by a fixed (wired) transport network.

Cell size:

• Highly variable.

• Technology dependent.

• Varies with expected number of users.

In telecommunication, a public land mobile network (PLMN) is a combination of wireless communication services offered by a specific operator in a specific country. A PLMN typically consists of several cellular technologies like GSM/2G, UMTS/3G, LTE/4G, offered by a single operator within a given country, often referred to as a cellular network.

A PLMN is identified by a globally unique PLMN code, which consists of a MCC (Mobile Country Code) and MNC (Mobile Network Code).

FDD vs TDD

FDD: Frequency Division Duplex

TDD: Time Division Duplex

Advantages of TDD

It does not use paired spectrum. Hence it benefits operators in terms of efficient usage of spectrum.

It is used for dynamic resource requirements based on application and quality of service. This is possible due to dynamic allocation of time slots without changing the bandwidth once allocated. Hence TDD is best suited for unpaired spectrum scenarios requiring asymmetric data rates.

FDD does not allow special techniques like multiple antennas, multiple input-output (MIMO), and beamforming.

Disadvantages of TDD

As TDD operates based on allocated time slots, it requires stringent phase/time synchronization to avoid interference between UL (Uplink) and DL (Downlink) transmissions.

Uplink and downlink transmissions occur at different time instants at the same carrier frequency. As transmissions are not continuous, the required data rates can not be achieved as compared to FDD at similar distances from Base Station.

As TDD supports lesser distances compared to FDD, it needs more base stations to achieve a given coverage area.

Due to the requirements for more Base stations, deployment and operating costs are higher in TDD.

Cells and spectrum efficiency

Cell: Pros/Cons

Fundamental:

• Each cell handles interferences, coverage areas, etc... locally.

• Cell planning.

  • Cell size.

  • Frequency/code usage.

• Channels (logical/physical) reservation.

Advantages:

• more capacity.

• greater number of users.

• less power.

• more reliability (distributed system).

Disadvantages:

• Needs an interconnection network between cells.

• Needs to support Handovers!

• Needs to handle inter-cell interference!