TD切换到G网失败问题

测试时同一个地点主叫切换失败，被叫切换成功。
切换地点是一个拐角地方，在拐之前TD信号很好RSCP为-72dBm，拐了之后RSCP为-92dBm，手机发送切换请求，G网邻区中Rxlevel-82dBm，手机商法测量消息后，核心网返回handoverFromUTRANCommand-GSM(DL_DCCH）
手机直接回复handoverFromUTRANFailure(UL_DCCH)
3A门限为event3a
thresholdOwnSystem -86
thresholdOtherSystem -91
hysteresis 4
请问是啥原因造成的呢？

 我把上发失败的信令发下
 <?xml version="1.0" ?>
- <Message Title="handoverFromUTRANFailure(UL_DCCH)">
- <UL-DCCH-Message>
- <integrityCheckInfo>
  <messageAuthenticationCode>01011110111100111010001110010011</messageAuthenticationCode>

  <rrc-MessageSequenceNumber>10</rrc-MessageSequenceNumber>

  </integrityCheckInfo>


- <message>
- <handoverFromUTRANFailure>
  <rrc-TransactionIdentifier>3</rrc-TransactionIdentifier>

- <interRAT-HO-FailureCause>
  <physicalChannelFailure />

  </interRAT-HO-FailureCause>


  </handoverFromUTRANFailure>


  </message>


  </UL-DCCH-Message>


  </Message>