Wireless Oom » tfc

Show me an actual example of TF, TFS, TFCS, TFC

wirelessoom — Tue, 23 Jun 2009 15:23:02 +0000

Below is an example of transport characteristics of an interactive service through DCH

The below is an example of the transport characteristics of a Signaling Radio Bearer through DCH

These two DCHs are multiplexed into a CCTrCH with the following TFCS (transport format combination set).

For a given TTI, TFC (Transport format combination) is chosen and used.

TFC selection algorithm

wirelessoom — Thu, 18 Jun 2009 04:35:55 +0000

Q1. Which layer will decide TFC ?

Q2. What factors impact its decision?

A1: MAC layer

A2: Many factors

1. given current channel condition; if noisy channel, only some of the TFCs can be used

2. data buffers in the RLC layer

3. priority of the data in RLC buffer

RLC buffer is not a stream of bits, but a group of PDUs.

Remember, TFC selection algorithm must be done every 10ms (worst case).

The algorithm is vendor specific.

Is it OK to have different TTI values in multiplexed channel?

wirelessoom — Thu, 18 Jun 2009 04:13:19 +0000

Yes!

Transport format combination (TFC) selection frequency is equal to the length of the shortest configured TTI duration.

How does the receiver know transport format combination?

wirelessoom — Thu, 18 Jun 2009 04:09:38 +0000

During a given TTI, the selected transport formation combination (TFC) must reamin the same.

It can be changed by the transmitter from one TTI to another.

Such a change involves alterations in physical layer parameters suchas the spreading factor etc.

Thus, the receiver should detect the transport format combination that is being used at a given moment.

This can be done explicitly by means of TFCI (indicator), included in the control physical channels, or by means of blind detection procedures.

What is transport format combination in umts?

wirelessoom — Wed, 17 Jun 2009 23:29:23 +0000

So confusing with transport format, transport format set ?

The fact: Several transport channels can be multiplexed in a single physical channel.

So, transport format combination (TFC) defines the number of transport blocks that are transmitted from each of the multiplexed transport channels in a given TTI.

Example:

DCH1:

{10ms, turbo coding, static rate matching parameter =1}

{40 bits, 40 bits}

DCH2:

{10ms, convolutional coding, static rate matching parameter =3}

{320 bits, 320 bits}

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