February 2012 - Telecommunications Blog

A blog for mobile communications systems GSM , UMTS and LTE

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Monday, February 27, 2012

4G LTE air interface - Radio Frequency Aspects

2/27/2012 08:50:00 AM 0
4G LTE air interface - Radio Frequency Aspects
LTE air interface adopts OFDMA (orthogonal frequency division multiple access) for the downlink and SC-FDMA (single-carrier frequency domain multiple access) for the uplink. It employs AMC (adaptive modulation and coding) as well as a number of optional MIMO (multiple-input multiple-output) antenna techniques and interference management methods for potential performance enhancements.

Telecommunications Blog

One of the first things to note about LTE is the integration between the Frequency Division Duplex (FDD) and Time Division Duplex (TDD) radio access modes. In the previous Universal Mobile Telephone System (UMTS) specifications, which also supported FDD and TDD, the RF specifications for the UE FDD, UE TDD, base station FDD and base station TDD modes were covered in separate documents.

However, the early decision by 3GPP to fully integrate FDD and TDD modes for LTE has resulted in only one RF specification document each for the UE and the eNB. With the higher level of integration between the two modes, the effort required to support them should be less than it was in the past.

Channel Bandwidths:

LTE was designed from the start to support six different channel bandwidths. These are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. In addition to this the subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.

Earlier versions of the specifications also supported 1.6 MHz and 3.2 MHz for interworking with LCR TDD, but these were removed when the LTE TDD frame structure was aligned with the FDD frame structure rather than the TD-SCDMA frame structure from UMTS.

Saturday, February 4, 2012

INTRODUCTION TO RF PLANNING 2

2/04/2012 10:22:00 AM 1
INTRODUCTION TO RF PLANNING 2
TOOLS USED FOR RF PLANNING :

• Network Planning Tool
• CW Propagation Tool
• Traffic Modeling Tool
• Project Management Tool


Network Planning Tool :

• Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage,  doing  frequency planning  automatically,  creating neighbor lists etc.







•  With a database that takes into account data such as terrain, clutter, and  antenna radiation patterns,  as  well  as  an intuitive  graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

       – Design wireless networks
       – Plan network expansions
       – Optimize network performance
       – Diagnose system problems
• The major tools available in the market are Planet, Pegasos, Cell Cad.
• Also many vendors have developed Planning tools of their  own like Netplan by Motorola, TEMS by Ericsson and so on.