Preamble and Postamble - EPF

EPF_LOC Algorithm

4.4.3 Preamble and Postamble

If the HS-SCCH is received, the UE checks whether the HS-PDSCH is also correctly received and then reports an ACK or NACK in the first slot of the HS-DPCCH subframe. If the HS-SCCH is erroneously received, the UE does not report any information in the first slot of the HS-DPCCH subframe. This type of transmission is called DTX. In the case of high interference, the NodeB may demodulate DTX as ACK by mistake when demodulating the HS-DPCCH. Therefore, the lost data blocks cannot be retransmitted through HARQ retransmission, and the reception can be ensured only through RLC retransmission. To meet the requirement of the 3GPP specifications for a low DTX misjudgment probability, more power has to be allocated for HS-DPCCH ACK/NACK.

To solve this problem, 3GPP TS 25.214 introduces preamble and postamble (WRFD-01061113

HS-DPCCH Preamble Support). When the NodeB demodulates an HS-DPCCH ACK/NACK, it considers the subframe prior to and the subframe next to the HS-DPCCH subframe in addition to the HS-DPCCH subframe itself. Therefore, for a certain DTX misjudgment probability, the introduction of preamble and postamble reduces the power required by ACK/NACK, lower the downlink load level, and increase the uplink capacity.

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4.5 TFRC Selection

The TFRC selection algorithm handles the MAC-hs queues in descending order of their priorities determined by the scheduler. In each TTI, the TFRC entity of a cell selects one or multiple queues and does the following:

 _{Determining the amount of data that can be transmitted by the queue or queues}  _{Determining the modulation scheme of the queue or queues}

 _{Allocating appropriate power and channelization codes to the queue or queues}

The basic procedure for the TFRC selection algorithm is as follows:

1. Based on the CQI reported by the UE, available power, and available channelization codes, the algorithm searches a CQI mapping table for the TBSmax, that is, the maximum MAC-hs transport block size (TBS). Note that the available power for every HSDPA user is restricted by

MXPWRPHUSR.

2. Based on the TBSmax and the amount of data buffered in the queue, the algorithm determines the most appropriate MAC-hs TBS (TBSused).

If the data buffered in the MAC-hs queue is enough to fill the space for carrying data in a transport block with the TBSmax, then the TBSmax is taken as the TBS to be used (TBSused). The TBSmax,

however, may be much larger than the data buffered in the MAC-hs queue. If this TBS is used, too many padding bits reduce the spectrum efficiency. To solve this problem, the algorithm searches the CQI mapping table backward for the CQI or the number of codes to obtain the most appropriate TBS and the corresponding modulation scheme. This TBS should be the smallest one in the TBS set that can carry the buffered data. The power and code resources determined through backward searching are taken as the ones for allocation.

3. Based on the TBSused, the algorithm determines the most appropriate power, codes, and modulation scheme.

Huawei supports three backward-searching methods, which are specified by the parameter RscAllocM

on the NodeB side:

 _{If the parameter is set to Code_Pri, the TFRC algorithm prefers the use of codes. Under the}

precondition that the transport block with the TBS is large enough to carry the buffered data, the algorithm first reduces the power. If the corresponding CQI decreases to the smallest one but the precondition is still met, the algorithm attempts to reduce the number of codes. This setting is applicable the outdoor macro base station with limited power.

 _{If the parameter is set to Power_Pri, the TFRC algorithm prefers the use of power. Under the}

precondition that the transport block with the TBS is large enough to carry the buffered data, the algorithm first reduces the number of codes. If the number of codes decreases to 1 but the

precondition is still met, the algorithm attempts to reduce the power. This setting is applicable to indoor application with limited codes.

 _{If the parameter is set to PowerCode_Bal, the TFRC algorithm balances the use of power and the use}

of codes. Under the precondition that the transport block with the TBS is large enough to carry the buffered data, the algorithm reduces the power and codes in a balanced mode. This setting protects the codes or power from being used up, improving the resource usage and increasing the cell capacity.

Figure 4-6 shows the backward-searching methods used when the parameter is set to Code_Pri or Power_Pri.

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Figure 4-6 Backward-searching methods used when the parameter is set to Code_Pri or Power_Pri

Figure 4-7 shows the backward-searching methods used when the parameter is set to PowerCode_Bal.

Figure 4-7 Backward-searching methods used when the parameter is set to PowerCode_Bal

In document HSDPA(RAN14.0_04).pdf (Page 35-37)