RAB Overview - TDSCDMA

 

 

 

The overall structure of Radio Bearer Configurtion for WCDMA and TDSCDMA are almost same. The major difference between WCDMA and TDSCDMA is physical layer (DPCH Uplink, DPCH Downlink). So in this page, I would describe mostly on physical layer configuration of TDSCDMA RAB. For the layers above the physical layer, refer to WCDMA RAB Overview and WCDMA R99 Radio Bearer.

 

Since most of the details above the physical layer is almost same as WCDMA, I would put some bullets here only for physical layer.

 

Frame Structure

 

Before you look into the details of Radio Bearer, you need to have very detailed understanding of Frame Structure. This is pretty big topics. So I posted it in separate page titled as 'Frame Structure'

 

 

Spreading Factor

 

Most of details in this section is based on 3GPP 25.221 V8.7.0 (2010-02)

 

< DPCH - Downlink >

 

You can use only two different SF for downlink (SF = 16, SF = 1). Refer to 25.221 5.2.1.1 Spreading for Downlink Physical Channels for details.

  • With SF = 16
    • Multiple parallel physical channels can be used to support higher data rates
    • These parallel physical channels shall be transmitted using different channelisation codes
  • With SF = 1
    • Only single code can be used

< DPCH - Uplink >

 

You can use any spreading factor from 16 to 1. (Refer to 25.211 5.2.1.2 Spreading for Uplink Physical Channels for details).

  • For each physical channel an individual minimum spreading factor SFmin is transmitted by means of the higher layers
  • For multicode transmission a UE shall use a maximum of two physical channels per timeslot simultaneously. These two parallel physical channels shall be transmitted using different channelisation codes

 

< P-CCPCH >

 

You can use only one spreading factor (SF = 16)

  • P-CCPCH1 can use only one channelization Code C(k=1, Q=16)
  • P-CCPCH2 can use only one channelization Code C(k=2, Q=16)

 

< S-CCPCH >

 

You can use only one spreading factor (SF = 16) except MBSFN slots

 

< FPACH >

 

You can use only one spreading factor (SF = 16)

 

< PRACH >

 

You can use SF=16, SF=8 or SF=4 and SIB (BCH message) will specify which SF should be used.

 

< HS-PDSCH >

 

You can use SF = 16 or SF = 1 if it is not for MIMO.

  • For the UEs configured in MIMO mode, if SF=16 is configured by higher layers to be not supported for dual stream transmission, the HS-PDSCH shall use spreading factor SF=1 only. Otherwise, the HS-PDSCH shall use either spreading factor SF = 16 or SF=1

 

< HS-SCCH >

 

You can use only one spreading factor (SF = 16)

 

< HS - SICH >

 

You can use only one spreading factor (SF = 16) with some exception on MIMO case.

  • When MIMO dual-stream is transmitted, the HS-SICH shall use spreading factor SF=8 which shall utilize an additional SF=16 channelisation code along the branch with the higher code numbering of the allowed OVSF sub tree.

 

< PLCCH >

 

You can use only one spreading factor (SF = 16)

  • Speading Code is specified by higher layer

< E-PUCH >

 

You can use SF = 1,2,4,8,16 but you have to use the same SF for all E-PUCH within the same TTI.

For scheduled transmissions, E-PUCHs use the spreading factor specified by CRRI on E-AGCH.

 

< E-RUCCH >

 

You can use SF = 16 or SF = 8.

The set of admissible spreading codes used on the E-RUCCH are based on the spreading codes of PRACH

 

< E-AGCH >

 

You can use only one spreading factor (SF = 16)

 

< E-HICH >

 

You can use only one spreading factor (SF = 16)

  • Multiple users’ signature sequences (including the inserted spare bits) sharing the same channelisation code are combined

 

 

Master Plan for Physical Layer

 

 

 

Guidelines for RAB Modification

 

One of the common request that I was getting was to create a new radio bearer or change a certain parameter of existing bearer. Unfortunately, this kind of request comes with a lot of missing information. If they provide full details of radio bearer parameters as described in 3GPP sample radio bearer definition, it would be relatively easy (too be honest.. it is not easy even with all those information.. but at least it is possible), but if they put out those request with a lot of missing information. If have to figure out on my own following things.

    i) Is the parameter that is requested to be changed correlated to any other parameters ?

    ii) If the parameter has correlation to other parameter, it is one-to-one type of correlation ? or if any changes are ok as long as it falls into a certain range

Let's suppose we have following request.

    a) I want you to change the number of channelization code from 8 to 10 in my existing bearer.

    b) I want you to change the number of slots from 1 to 2 in my existing bearer.

    c) I want you to change the slot fromat from 8 to 3 in my existing bearer.

If I take the request a), do I only have to change the number of channelization code for each slot ? or do I have to change some other parameter like TFS definition or any other transport/higher layer parameter ?

You may ask similar question for the request b) or c).

 

General guide line for this situation is as follows.

 

First, figure out the maximum total databits per radio frame(10 ms) based on TFCS setting. This become the input data size of transport channel process.

Second, figure out the totoal databits for radio frame (10 ms) based on physical layer configuration. This becomes the size of the output of transport channel process.0

 

 

Theoretically, if the output data size (2) of transport process is greater than input data size (1), any change in PHY layer or transport layer parameter are acceptable.

 

In reality, you may need a little bit further detailed guide lines case by case, but this can be a good first step guide line and at least it will relieve some panic -:)

 

Examples of common Radio Bearer with focus on Physical Layer Configuration